U.S. patent application number 10/555465 was filed with the patent office on 2007-01-25 for treatment of nucleic acid.
Invention is credited to Douglas Spencer Millar, Cassandra Jean Vockler.
Application Number | 20070020633 10/555465 |
Document ID | / |
Family ID | 33310375 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070020633 |
Kind Code |
A1 |
Millar; Douglas Spencer ; et
al. |
January 25, 2007 |
Treatment of nucleic acid
Abstract
The invention provides methods for treating nucleic acid,
particularly nucleic acid that is methylated. In one embodiment,
the method can include the steps of (a) providing a denaturing
environment to a nucleic acid sample; (b) reacting the nucleic acid
sample with a bisulphite reagent and incubating the reaction so as
to form a treated nucleic acid sample where methylated nucleotides
in the nucleic acid sample remain unchanged while unmethylated
nucleotides are converted to another form; (c) diluting the treated
nucleic acid sample so as to reduce salt concentration to a level
which will not substantially interfere with a nucleic acid
precipitating step; (d) precipitating the diluted treated nucleic
acid to substantially remove any unwanted reagents or diluents from
treated nucleic acid; and (e) carrying out de-sulphonation of the
precipitated treated nucleic acid so as to remove sulphonate groups
present on the treated nucleic acid so as to obtain a nucleic acid
sample substantially free of sulphonate groups.
Inventors: |
Millar; Douglas Spencer;
(New South Wales, AU) ; Vockler; Cassandra Jean;
(New South Wales, AU) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
33310375 |
Appl. No.: |
10/555465 |
Filed: |
April 29, 2004 |
PCT Filed: |
April 29, 2004 |
PCT NO: |
PCT/AU04/00549 |
371 Date: |
August 28, 2006 |
Current U.S.
Class: |
435/6.14 ;
536/25.4 |
Current CPC
Class: |
C12Q 1/68 20130101; C12Q
1/6827 20130101; C12Q 1/68 20130101; C07H 21/04 20130101; C12Q
1/6827 20130101; C12Q 2523/125 20130101; C12Q 2523/125 20130101;
C12Q 2527/119 20130101 |
Class at
Publication: |
435/006 ;
536/025.4 |
International
Class: |
C12Q 1/68 20060101
C12Q001/68; C07H 21/04 20070101 C07H021/04 |
Foreign Application Data
Date |
Code |
Application Number |
May 2, 2003 |
US |
10428310 |
Claims
1-27. (canceled)
28. A method for treating nucleic acid comprising: (a) providing a
denaturing environment to a nucleic acid sample; (b) reacting the
nucleic acid sample with a bisulphite reagent and incubating the
reaction so as to form a treated nucleic acid sample where
methylated nucleotides in the nucleic acid sample remain unchanged
while unmethylated nucleotides are converted to another form; (c)
diluting the treated nucleic acid sample so as to reduce salt
concentration to a level which will not substantially interfere
with a nucleic acid precipitating step; (d) precipitating the
diluted treated nucleic acid to substantially remove any unwanted
reagents or diluents from the treated nucleic acid sample; and (e)
carrying out de-sulphonation of the precipitated treated nucleic
acid so as to remove sulphonate groups present on the treated
nucleic acid so as to obtain a nucleic acid sample substantially
free of sulphonate groups.
29. The method according to claim 28 wherein more than about 50% of
the starting nucleic acid in the sample is retained.
30. The method according to claim 29 wherein more than about 75% of
the starting nucleic acid in the sample is retained.
31. The method according to claim 30 wherein more than about 95% of
the starting nucleic acid in the sample is retained.
32. The method according to claim 28 further comprising: (f)
processing or analysing the treated nucleic acid sample.
33. The method according to claim 28 wherein the sample comprises
DNA, the sample comprises RNA, or the sample comprises combination
of both DNA and RNA.
34. The method according to claim 28 wherein the sample is prepared
from tissue, organ, cell, microorganism, biological sample, or
environmental sample.
35. The method according to claim 28 carried out in a reaction
vessel. The method according to claim I wherein the bisulphite
reagent is sodium metabisulphite.
36. The method according to claim 35 wherein the reaction vessel is
selected from the group consisting of tube, plate, capillary tube,
well, centrifuge tube, microfuge tube, slide, coverslip, and
surface.
37. The method according to claim 28 wherein the denaturing
environment is provided to the sample by adding an alkali.
38. The method according to claim 28 wherein the denaturing
environment is provided to the sample by adding an alkali.
39. The method according to claim 38 wherein the alkali is NaOH,
KOH, or any compound or agent providing hydroxyl groups.
40. The method according to claim 28 wherein the denaturing
environment is provided to the sample by heating.
41. The method according to claim 40 wherein the heating is up to
about 95.degree. C.
42. The method according to claim 41 wherein the heating is from
50.degree. C. to 70.degree. C.
43. The method according to claim 28 wherein the providing step (a)
is carried out in the presence of an additive capable of enhancing
the bisulphite reaction.
44. The method according to claim 43 wherein the additive is
selected from the group consisting of quinol, urea, methoxyamine,
and mixtures thereof.
45. The method according to claim 28 wherein the reacting step (b)
results in methylated cytosines in the nucleic acid sample
remaining unchanged while unmethylated cytosines are converted to
uracils.
46. The method according to claim 28 wherein the dilution step (c)
is carried out using water to reduce salt concentration to below
about 0.5 M.
47. The method according to claim 28 wherein the precipitation is
carried out using an alcohol precipitating agent.
48. The method according to claim 47 wherein the alcohol
precipitating agent is selected from the group consisting of
isopropanol, ethanol, butanol, methanol, and mixtures thereof.
49. The method according to claim 48 wherein the alcohol is
isopropanol.
50. The method according to claim 28 wherein the de-sulphonation
step (d) is carried out by adjusting the precipitated treated
nucleic acid up to about pH 12.5 with a buffer or alkaline
reagent.
51. The method according to claim 50 wherein the pH is adjusted to
about 10.5.
52. A kit for carrying out the method according to claim 28
comprising vessels containing reagents and instructions to use the
reagents.
53. The kit according to claim 52 wherein the reagents comprise a
diluent, a bisulphite reagent and an alkali.
54. The kit according to claim 53 wherein the bisulphite reagent is
sodium metabisulphite.
Description
TECHNICAL FIELD
[0001] The present invention relates to modified methods for
treating nucleic acid, particularly methylated nucleic acid using
bisulphite.
BACKGROUND
[0002] As a result of advances in automated sequencing technology,
much work has been carried out on determining coding regions of DNA
resulting in the full sequencing of many animal genomes including
the human genome. It has been realised for many years that the
majority of genomic DNA, however, is non-coding and this material
was once considered as "junk" DNA. Analysis of the non-coding
regions of DNA is now being considered as important in the study of
gene expression and function. Methylation states or patterns in
nucleic acid, particularly genomic DNA, is thought to have a
functional or regulatory role in gene expression and control in
animals.
[0003] It has been demonstrated that, in single stranded DNA,
sodium bisulphite preferentially deaminates cytosine to uracil,
compared to a very slow rate of deamination of 5-methylcytosine to
thymine (Shapiro, R., DiFate, V., and Welcher, M, (1974) J. Am.
Chem. Soc. 96: 906-912). This observation served as the basis for
the development of the bisulphite genomic sequencing protocol of
Frommer et al 1992 [Frommer M, McDonald L E, Millar D S, Collis C
M, Watt F, Grigg G W, Molloy P L and Paul C L. PNAS 89: 1827-1831
(1992), which is incorporated herein by reference]. In summary,
this method as presently practiced involves the following general
steps: alkaline denaturation of DNA; deamination using sodium
bisulphite; desulphonation by desalting followed by sodium
hydroxide treatment; neutralization and desalting.
[0004] One of the major disadvantages of the bisulphite.
modification procedure and the established variation thereof is
that it has been shown that the procedure results in the
degradation of between 84-96% of the original input DNA (Grunau et
al. Nucleic Acids Research 29 (13) e65; (2001). The high loss
associated with the procedure means that practically it is very
difficult to successfully analyse small numbers of cells for their
methylation status, or successfully analyse ancient archival
specimens in which the DNA is already in a partially degraded
state. In addition, due to inherent degradation of the current
methods, it is not possible to sequence and assemble the complete
genome of an organism to determine its genome-wide methylation
profile in the same manner as has been successfully applied by the
public Human Genome Project (International Human Genome Sequencing
Consortium, 2001, Nature, 409, 860-921) or the private CELERA
sequencing project (J Craig Venter et al., 2001, Science, 291,
1304-1351) as the DNA would be so fragmented as it would not be
able to be cloned, sequenced, and assembled in any meaningful way
owing to the huge number of "gaps" in the sequence.
[0005] A further disadvantage with the bisulphite method as
presently practiced is that, in general, only small fragments of
DNA can be amplified. Experience shows that generally less than
about 500 base pairs (bp) can be successfully treated and
amplified. The present technique is not applicable to new molecular
biological methods such as Long Distance polymerase chain reaction
(PCR) which has made it possible to amplify large regions of
untreated genomic DNA, generally up to about 50 kb. At present, it
is not even possible to analyse the methylation status of intact
genes, as a large number of genes in mammalian genomes exceed 50 kb
in length.
[0006] To look at the methylation status of even relatively small
genes (<4 kb), PCR reactions have had to be staggered across the
gene region of interest (D. S Millar, K. K Ow, C. L. Paul, P. J.
Russell, P. L. Molloy, S. J. Clark, 1999, Oncogene, 18(6):1313-24;
Millar D S, Paul C L, Molloy P L, Clark S J. (2000). J Biol Chem;
275(32):24893-9). The methods presently used for bisulphite DNA
treatment have also been laborious and time consuming. Standard
methods typically require multiple tube changes, column
purifications, dialysis, embedding the DNA in agarose beads or the
addition of additives to the reaction in an attempt to reduce
problems such as non-conversion of certain regions of genomic DNA.
Thus a more reliable method that does not lead to substantial DNA
degradation, and which overcomes or at least reduces the multiple
problems associated with present DNA treatment, is required.
DISCLOSURE OF INVENTION
[0007] The invention relates to an improved bisulphite treatment
method of nucleic acids which is efficient, adaptable for use with
many different molecular biological techniques, and can achieve
significant retention of nucleic acid, which is herein termed the
Human Genetic Signatures (HGS) bisulphite method or the method of
present invention.
[0008] The invention provides, in one embodiment, a method for
treating nucleic acids. The method can include the steps of
denaturing a nucleic acid sample; incubating the nucleic acid
sample with a bisulphite reagent, thereby modifying methylated
nucleotides with sulphonate groups; diluting the modified nucleic
acid sample; precipitating the modified nucleic acid sample; and
reacting the modified nucleic acid sample to remove sulphonate
groups. The denaturation of the nucleic acid can be performed, for
example, by treatment with alkali.
[0009] In another embodiment, the present invention provides a
method for treating nucleic acid comprising: [0010] (a) providing a
denaturing environment to a nucleic acid sample; [0011] (b)
reacting the nucleic acid sample with a bisulphite reagent and
incubating the reaction so as to form a treated nucleic acid sample
where any methylated nucleotides in the nucleic acid sample remain
unchanged while unmethylated nucleotides are converted to another
form; [0012] (c) diluting the treated nucleic acid sample so as to
reduce salt concentration to a level which will not substantially
interfere with a nucleic acid precipitation step; [0013] (d)
precipitating the diluted treated nucleic acid to substantially
remove any unwanted reagents or diluents from the vessel; and
[0014] (e) carrying out de-sulphonation of the precipitated treated
nucleic acid so as to remove sulphonate groups present on the
treated nucleic acid so as to obtain a nucleic acid sample
substantially free of sulphonate groups without inducing
significant amounts of strand breakage.
[0015] The method typically retains more than about 50%, generally
more than about 75%, and can be more than about 95% of the starting
nucleic acid in the sample. The methods of the invention can be
carried out without causing any substantial degradation or loss of
the nucleic acid sample. In contrast, bisulphite methods presently
in use or described in the prior art typically result in loss of up
to about 96% of the nucleic acid sample so that only about 4% of
the nucleic acid is actually available for analysis.
[0016] The method may further comprise: [0017] (f) further
processing or analysing the treated nucleic acid sample.
[0018] The sample may include DNA or RNA or a combination of both
DNA and RNA.
[0019] Unlike prior art methods, there is no need to completely
separate or isolate the treated nucleic acid from the bisulphite
reagent. There is no need to employ chromatography separation
methods, for example, as presently required by prior art methods.
The dilution step according to the present invention assists in
minimizing loss of sample.
[0020] The present invention also relates to kits containing
reagents and instructions to carry out the method according to the
present invention.
[0021] Throughout this specification, unless the context requires
otherwise, the word "comprise", or variations such as "comprises"
or "comprising", will be understood to imply the inclusion of a
stated element, integer or step, or group of elements, integers or
steps, but not the exdusion of any other element, integer or step,
or group of elements, integers or steps.
[0022] Any discussion of documents, acts, materials, devices,
articles or the like which has been included in the present
specification is solely for the purpose of providing a context for
the present invention. It is not to be taken as an admission that
any or all of these matters form part of the prior art base or were
common general knowledge in the field relevant to the present
invention as it existed in Australia before the priority date of
each claim of this application.
[0023] In order that the present invention may be more clearly
understood, preferred embodiments will be described with reference
to the following drawings and examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 shows comparison of recovery of bisulphite-treated
DNA from various tissue samples between the HGS bisulphite method
and traditional bisulphite method (Clark et al., (1994) Nucleic
Acids Res. 22:2990-2997). Well #1, DNA extracted from 2 LNCaP cells
and treated with bisulphite; Well #2, DNA extracted from 20 LNCaP
cells and treated with bisulphite; Well #3, DNA extracted from 200
LNCaP cells and treated with bisulphite; Well #4, DNA extracted
from 2,000 LNCaP cells and treated with bisulphite; and Well #5,
DNA extracted from 20,000 LNCaP cells and treated with bisulphite.
The HGS method is shown on the left (lanes marked 1-5,
respectively, as indicated above); the traditional bisulphite
method is shown on the right (lanes marked 1-5, respectively, as
indicated above).
[0025] FIG. 2 shows results obtained using the HGS bisulphite
treatment on RNA extracted from the prostate cancer cell line Du145
compared to using the conventional bisulphite approach. Lane 1
untreated control RNA, Lane 2 bisulphite treated RNA at 4.degree.
C. overnight, Lane 3 bisulphite treated RNA at room temperature
overnight, Lane 4 bisulphite treated RNA at 55.degree. C.
overnight. Lane 5 bisulphite treated RNA at room temperature
overnight replicate #2, lane 6 bisulphite treated RNA at room
temperature overnight replicate #3. Lane 7 bisulphite treated RNA
at room temperature overnight using the conventional method (Clark
et al 1994). M=molecular size markers.
[0026] FIG. 3 shows a time course experiment on the stability of
the RNA using different temperature incubations. From the result it
can be seen that a small amount of degradation takes place in the
1.sup.st 30 minutes of incubation but then reaches an almost steady
state and very little is lost subsequently even after 16 hour
incubation at 55.degree. C.
[0027] FIG. 4 shows Reverse Transcriptase PCR performed on both
bisulphite converted RNA and wild type RNA. As can be seen strong
PCR amplification signals are seen in the bisulphite treated RNA at
the same size as the bands in the wild type RNA. Lane 1. RT-PCR
amplification using bisulphite primers to amplify exon 3 and 4 of
bisulphite treated human beta-actin RNA. Lane 2. RT-PCR
amplification using bisulphite primers to amplify exon 3 of
bisulphite treated human beta-actin RNA. Lane 3. RT-PCR
amplification using wild type primers to amplify exon 3 and 4 of
human beta-actin RNA. Lane 4. RT-PCR amplification using wild
primers to amplify exon 3 of human beta-actin RNA. M=size markers.
NB; no PCR amplification was observed when bisulphite treated
amplification primers were used on wild type RNA, and additionally
no PCR signals were observed when wild type primers were used on
bisulphite treated RNA.
[0028] FIG. 5 shows confirmation that the PCR products generated in
FIG. 4 were derived from the bisulphite treated genomic RNA. The
arrow shows the splice site between exon 3 and 4 in the human
beta-actin transcript.
MODE(S) FOR CARRYING OUT THE INVENTION
[0029] Embodiments for treating nucleic acid are described in
non-limiting detail below.
[0030] The invention provides methods for the treatment and
analysis of nucleic acids. The methods are advantageous in that
they provide a simple and highly efficient method for modification
of nucleic acids and can be used, for example, to examine the
methylation pattern or changes in methylation of genomic DNA or
RNA. The methods of the invention provide a simplified procedure
with higher yields and higher molecular weight nucleic acid
molecules relative to previously known methods, thus allowing the
analysis of smaller amounts of nucleic acids as well as easy
application to a large number of samples.
[0031] The invention provides a method for treating nucleic acid
comprising: [0032] (a) denaturing a nucleic acid sample; [0033] (b)
reacting the nucleic acid sample with a bisulphite reagent and
incubating the reaction so as to form a treated nucleic acid sample
where any methylated nucleotides in the nucleic acid sample remain
unchanged while unmethylated nucleotides are converted to another
form; [0034] (c) diluting the treated nucleic acid sample so as to
reduce salt concentration to a level which will not substantially
interfere with a nucleic acid precipitation step; [0035] (d)
precipitating the diluted treated nucleic acid to substantially
remove any unwanted reagents or diluents from treated nucleic acid
sample; and [0036] (e) carrying out de-sulphonation of the
precipitated treated nucleic acid so as to remove sulphonate groups
present on the treated nucleic acid so as to obtain a nucleic acid
sample substantially free of sulphonate groups.
[0037] The denaturation of the nucleic acid sample can be
performed, for example, by providing an alkali environment to a DNA
sample. The methods are particularly useful in the analysis of DNA
nucleic acid samples. The denaturation of RNA samples can be
carried out by heating the RNA to resolve secondary structure.
Heating typically is up to about 95.degree. C., preferably between
about 50.degree. C. to 70.degree. C. It will be appreciated,
however, that the temperature is selected to preferably denature
the RNA to remove secondary structure but not destroy or disrupt
the RNA molecule.
[0038] The desulphonation step is generally carried out under
controlled conditions so as to remove sulphonate groups present on
the treated nucleic acid sample. The methods are advantageous
because they can be performed so that the nucleic acid sample, for
example, strands of DNA, are not broken or sheared to a significant
extent. Such methods are particularly advantageous for RNA samples
as addition of alkali as described in the traditional bisulphite
procedure would result in total RNA degradation.
[0039] The invention thus provides, in one embodiment, a method for
treating nucleic acids. The method can include the steps of
denaturing a nucleic acid sample; incubating the nucleic acid
sample with a bisulphite reagent, thereby modifying methylated
nucleotides with sulphonate groups; diluting the modified nucleic
acid sample; precipitating the modified nucleic acid sample; and
reacting the modified nucleic acid sample to remove sulphonate
groups. The denaturation of the nucleic acid can be performed, for
example, by treatment with alkali, heating, or addition of other
chemical or protein reagents that result in the formation of single
stranded nucleic acids.
[0040] The method typically results in more than about 50%,
generally more than about 75%, and can result in more than about
95% of the starting nucleic acid in the sample being retained. The
present inventors have found that the method can be carried out
without causing any substantial degradation or loss of the nucleic
acid sample. In contrast, bisulphite methods presently in use or
described in the prior art typically result in loss of up to about
96% of the nucleic acid sample.
[0041] The method may further comprise: [0042] (f) processing or
analysing the treated nucleic acid sample.
[0043] The sample may include DNA or RNA or a combination of both
DNA and RNA.
[0044] The sample can be prepared from tissue, cells or can be any
biological sample such as blood, urine, faeces, semen,
cerebrospinal fluid, lavage, cells or tissue from sources such as
brain, colon, urogenital, lung, renal, hematopoietic, breast,
thymus, testis, ovary, uterus, tissues from embryonic or
extra-embryonic linages, environmental samples, plants,
microorganisms including bacteria, intracellular parasites virus,
fungi, protozoan, viroid and the like. The best described mammalian
cell types suitable for treatment by the present invention are
summarized in B. Alberts et al., 1989, The Molecular Biology of the
Cell, 2.sub.nd Edition, Garland Publishing Inc New York and London,
pp 995-997.
[0045] The analysis of 5-methyl cytosine residues in DNA or RNA
from samples of human, animal, plant, bacterial, and viral origin
is meant to cover all life cycle stages, in all cells, tissues and
organs from fertilization until 48 hours post mortem, as well as
samples that may be derived from histological sources, such as
microscope slides, samples embedded in blocks, bodily fluids or
samples extracted from synthetic or natural surfaces or from
liquids.
[0046] The analyses are meant to include the naturally occurring
variation between cells, tissues and organs of healthy individuals,
(health as defined by the WHO), as well as cells, tissues and
organs from diseased individuals. Diseased in this sense includes
all human diseases, afflictions, ailments and deviant conditions
described or referred to in Harrison's Principles of Internal
Medicine, 12th Edition, edited by Jean D Wilson et al., McGraw Hill
Inc, and subsequent later editions; as well as all diseases,
afflictions ailments and deviant conditions described in OMIM
(Online Mendelian Inheritance in Man, www.ncbi.gov), but with
emphases on the leading causes of death, namely, malignant
neoplasms, (cancer), ischaemic heart disease, cerebrovascular
disease, chronic obstructive pulmonary disease, pneumonia and
influenza, diseases of arteries, (including atherosclerosis and
aortic aneurysm), diabetes mellitus, and central nervous system
diseases, together with socially debilitating conditions such as
anxiety, stress related neuropsychiatric conditions and obesity,
and all conditions arising from abnormal chromosome number or
chromosome rearrangements, (aneuploidy involving autosomes as well
as sex chromosomes, duplications, deficiencies, translocations and
insertions), as well as similar abnormalities of the mitochondrial
genomes.
[0047] The normal or diseased individuals may be from (i)
populations of diverse ethnicity and evolutionary lineages; (ii)
strains and geographical isolates; (iii) sub species; (iv) twins or
higher order multiplets of the same or different sex; (v)
individuals arising from normal methods of conjugation, artificial
insemination, cloning by embryonic stem cell methods, or by nuclear
transfer, (from somatic or germ line nuclei), or from the input or
modification of mitochondrial or other cellular organelles; (vi)
individuals deriving from transgenic knock-out, knock-in or
knock-down methods, (either in vivo, ex vivo, or by any method in
which gene activity is transiently or permanently altered, e.g., by
RNAi, ribozyme, transposon activation, drug or small molecule
methodologies, Peptide Nucleic Acid (PNA), Intercalating Nucleic
Acid (INA), Altritol Nucleic Acid (ANA), Hexitol Nucleic Acid
(HNA), Locked Nucleic Acid (LNA), Cyclohexanyl Nucleic Acid (CNA),
and the like, or nucleic acid based conjugates, including but not
restricted to Trojan peptides, or individuals at any stages of
pregnancy, normal or ectopic.
[0048] The analyses also include 5-methyl cytosine residues in DNA
or RNA from prokaryotic or eukaryotic organisms and viruses (or
combinations thereof), that are associated with human diseases in
extracellular or intracellular modes, for the purposes of
determining, and therapeutically altering, in both normally varying
and diseased systems, the changed parameters and underlying
mechanisms of: [0049] (I) genetic diseases; [0050] (II) non-genetic
or epigenetic diseases caused by environmentally induced factors,
be they of biological or non-biological origin, (environmental in
this sense being taken to also include the environment within the
organism itself, during all stages of pregnancy, or under
conditions of fertility and infertility treatments); [0051] (III)
predisposition to genetic or non genetic diseases, including
effects brought about by the "prion" class of factors, by exposure
to pressure changes and weightlessness, or by radiation effects;
[0052] (IV) 5-methyl cytosine changes in the processes of aging in
all cell types, tissues, organ systems and biological networks,
including age related depression, pain, neuropsychiatric and
neurodegenerative conditions and pre- and post-menopausal
conditions, (including reduced fertility; in both sexes); [0053]
(V) 5-methyl cytosine changes in cancer, (including changes in
cells with abnormal karyotypes arising from DNA amplification,
deletion, rearrangement, translocation and insertion events), and
their variations or alterations in different cell cycle phenomena
(including cell cycle effects on diumal rhythms, photoperiod,
sleep, memory, and "jet lag"; [0054] (VI) 5-methyl cytosine changes
in metabolic networks defined in the broadest sense, from the
zygote through embryogenesis, foetal development, birth,
adolescence, adulthood and old age (including metabolic effects
brought about by hypoxia, anoxia, radiation of any type, (be it
ionizing or non ionizing, or arising from chemotherapeutic
treatments, high altitude exposure radiation from nearby natural
sources, such as rocks or from "fallout" from military or
government sponsored activities), stress, or by imbalances between
the mitochondrial, nuclear or organellar genomes; (VII) 5-methyl
cytosine alterations due to responses at the molecular, cellular,
tissue, organ and whole organism levels to proteins, polypeptides,
peptides, and DNA, RNA, PNA, INA, ANA, HNA, LNA, CNA, and the like,
or peptide aptamers (including any with post translational
additions, post translational cleavage products, post translational
modifications (such as inteins and exeins, ubiquination and
degradation products); proteins, polypeptides and peptides
containing rare natural amino acids, as well as single rare amino
acids such as D-serine involved in learning, brain growth and cell
death; drugs, biopharmaceuticals, chemical entities (where the
definitions of Chemical Entities and Biopharmaceuticals is that of
G. Ashton, 2001, Nature Biotechnology 19, 307-3111)), metabolites,
new salts, prodrugs, esters of existing compounds, vaccines,
antigens, polyketides, non-ribosomal peptides, vitamins, and
molecules from any natural source (such as the plant derived
cyclopamine); [0055] (VIII) 5-methyl cytosine alterations due to
responses at the molecular, cellular, tissue, organ and whole
organism levels to RNA and DNA viruses be they single or double
stranded, from external sources, or internally activated such as in
endogenous transposons or retrotransposons, (SINES and LINES);
[0056] (IX) 5-methyl cytosine alterations due to responses at the
molecular, cellular, tissue, organ and whole organism levels to
reverse transcribed copies of RNA transcripts be they of genic or
non genic origins, (or intron containing or not); [0057] (X)
5-methyl cytosine alterations due to responses at the molecular,
cellular, tissue, organ and whole organism levels to: (a) DNA, RNA,
PNA, INA, ANA, HNA, LNA, CNA, and the like (or DNA, RNA, PNA, INA,
ANA, HNA, LNA, CNA, aptamers of any in all combinations); including
DNA, RNA, PNA, INA, ANA, HNA, LNA, CNA, and the like molecules
circulating in all fluids including blood and cerebrospinal fluid
as well as maternal fluids before, during and after pregnancy (b)
combinations of conjugated biomolecules that are chimeras of
peptides and nucleic acids; or chimeras of natural molecules such
as cholesterol moieties, hormones and nucleic acids; and [0058]
(XI) 5-methyl cytosine alterations due to responses of stem cells,
(either in vivo, ex vivo or in association with novel environments
or natural and synthetic substrates (or combinations thereof), from
human and animal origin to any of the perturbations described in
(i) to (x) above.
[0059] Any suitable method for obtaining nucleic acid material can
be used. Examples include, but are not limited to, commercially
available DNA/RNA kits or reagents, workstation, standard cell
lysis buffers containing protease reagents and organic extraction
procedures, which are well known to those of skill in the art.
[0060] The method can be carried out in a reaction vessel. The
reaction vessel can be any suitable vessel such as tube, plate,
capillary tube, well, centrifuge tube, microfuge tube, slide,
coverslip or any suitable surface. The method is generally carried
out in one reaction vessel in order to reduce the likelihood of
degradation or loss of the nucleic acid sample.
[0061] Generally, the denaturing environment is provided to the
sample by adding either an alkali such as NaOH or by heating the
nucleic acid containing sample. The alkali environment is provided
to denature double stranded DNA acid molecules into a state where
the molecules are readily reactive with the bisulphite reagent. It
will be appreciated, however, that any other denaturation method
such as heat treatment or other suitable alkali or denaturing agent
can be added or used such as KOH and any other alkali so long as
use of the reagents for denaturation do not significantly inhibit
subsequent steps. This can be important for RNA analysis as alkali
results in degradation of the RNA molecules therefore another
method such as heat denaturation is therefore desirable.
[0062] Generally, the bisulphite reagent is sodium metabisulphite.
The bisulphite reagent is used to cause sulphonation of cytosine
bases to cytosine sulphonate followed by hydrolytic deamination of
the cytosine sulphonate to uracil sulphonate. It will be
appreciated, however, that any other suitable bisulphite reagent
could be used such as sulphite or acetate ions (see Shapiro, R.,
DiFate, V., and Welcher, M, (1974) J. Am. Chem. Soc. 96:
906-912).
[0063] The incubation with the sulphonating reagent can be carried
out at pH below 7 and at a temperature which favors the formation
of the uracil sulphonate group. A pH below about 7 is preferred for
carrying out the sulphonation reaction, which converts the cytosine
bases to cytosine sulphonate and subsequently to uracil sulphonate.
However, the methods of the invention can be performed with the
sulphonation reaction above pH 7, if desired.
[0064] The sulphonation reaction can be carried out in the presence
of an additive capable of enhancing the bisulphite reaction.
Examples of suitable additives include, but not limited to, quinol,
urea, methoxyamine. Of these reagents, quinol is a reducing agent.
Urea and methyoxyamine are agent added to improve the efficiency of
the bisulphite reaction. It will be appreciated that other
additives or agents can be provided to assist in the bisulphite
reaction.
[0065] The sulphonation reaction results in methylated cytosines in
the nucleic acid sample remaining unchanged while unmethylated
cytosines are converted to uracils.
[0066] Reaction conditions found to work well are as follows. The
denatured DNA, or other nucleic acids, to be treated is made up to
a volume of 20 .mu.l. Then 208 .mu.l of a freshly prepared solution
of 2 M sodium metabisulphite (BDH AnalaR #10356.4D) pH 5.0 (the pH
is adjusted by the addition of 10M sodium hydroxide (BDH AnalaR
#10252.4X) along with 12 .mu.l of a 10 mM quinol solution (BDH
AnalaR #103122E). The concentration of quinol added can be anything
in the range of about 10 to 500 mM as determined experimentally.
The solution is then mixed and overlayed with 208 .mu.l of mineral
oil (Sigma molecular biology grade M-5904). The sample is then left
overnight at a suitable temperature, for example, room temperature
or another suitable temperature, to allow time for full bisulphite
conversion. It is understood by those skilled in the art that the
volumes, concentrations and incubation time and temperature
described above are merely exemplary and can be varied so long as
the reaction conditions are suitable for sulphonation of the
nucleic acids. It is also understood that the order of the steps of
methods of the invention can be varied so long as the sulphonation
and desulphonation steps are sufficiently carried out.
[0067] The dilution step is performed so that the salts inhibitory
to subsequent reactions are not co-precipitated with the
sulphonated nucleic acids. The salt concentration is diluted to
less than about 1 M. Generally, the dilution step is carried out
using water or buffer to reduce the salt concentration to below
about 0.5M. For example, the salt concentration is generally
diluted to less than about 1 mM to about 1 M, in particular, less
than about 0.5 M, less than about 0.4 M, less than about 0.3 M,
less than about 0.2 M, less than about 0.1 M, less than about 50
mM, less than about 20 mM, less than about 10 mM, or even less than
about 1 mM, if desired. One skilled in the art can readily
determine a suitable dilution that diminishes salt precipitation
with the nucleic acids so that subsequent steps can be performed
with minimal further clean up or manipulation of the nucleic acid
sample. The dilution is generally carried out in water but can be
carried out in any suitable buffer, for example Tris/EDTA or other
biological buffers so long as the buffer does not precipitate
significantly or cause the salt to precipitate significantly with
the nucleic acids so as to inhibit subsequent reactions.
[0068] Unlike prior art methods, there is no need to completely
separate or isolate the treated nucleic acid from the bisulphite
reagent. There is no need to employ chromatography separation
methods, for example, as presently required by prior art methods.
The dilution step according to the present invention assists in
minimizing loss of sample.
[0069] Generally, precipitation is carried out using a
precipitating agent such as an alcohol. An exemplary alcohol for
precipitation of nucleic acids can be selected from isopropanol,
ethanol or any other suitable alcohol.
[0070] The de-sulphonation step can be carried out by adjusting the
pH of the precipitated treated nucleic acid up to about 12.5.
Exposure to alkaline environments tends to promote strand breaks in
apurinic sites in the nucleic acid induced by the previous exposure
to an acidic pH. Therefore, the alkaline pH treatment is minimized
if strand breaks are to be avoided. This step can be carried out
efficiently at around pH 10.5 with a suitable buffer or alkali
reagent. Examples of suitable buffers or alkali reagents include
buffers having a pH 7.0-12.5. It will be appreciated by persons
skilled in the art that suitable buffers or alkali reagents can be
selected from the vast range of known buffers and alkali reagents
available.
[0071] Temperature ranges for the de-sulphonation step are room
temperature to about 96.degree. C. and times can vary from 2
minutes to 96 hours or longer depending on the conditions used. One
skilled in the art can readily determine a suitable time and
temperature for carrying out the de-sulphonation reaction.
Temperatures below room temperature can also be used so long as the
incubation time is increased to allow sufficient desulphonation.
Thus, the incubation step can be carried out at about 10.degree.
C., about 20.degree. C., about 22.degree. C., about 25.degree. C.,
about 30.degree. C., about 35.degree. C., about 37.degree. C.,
about 40.degree. C., about 45.degree. C., about 50.degree. C.,
about 55.degree. C., about 60.degree. C., about 65.degree. C.,
about 70.degree. C., about 75.degree. C., about 80.degree. C.,
about 85.degree. C., about 90.degree. C., about 95.degree. C., and
about 96.degree. C., A particularly useful temperature for carrying
out the desulphonation reaction is about 55.degree. C. These and
other incubation and/or reaction steps can be similarly carried out
at various temperatures, as described above, so long as a
sufficient reaction step is performed.
[0072] The present invention provides methods for the efficient
characterization of methylated nucleic acids. The methods allow
efficient sulphonation and desulphonation steps to be carried out
on the nucleic acid sample. However, it is understood that neither
of the sulphonation or desulphonation steps need be carried out to
completion, only sufficiently to subsequently characterize
methylation of the nucleic acid, as disclosed herein. One skilled
in the art can readily determine whether these steps should be
carried out to near completion or whether incomplete reactions are
sufficient for a desired analysis. For example, when a small number
of cells or a small amount of nucleic acid sample are used, it is
generally desired that a more complete reaction be performed. When
larger quantities of nucleic acid sample are being characterized, a
less complete reaction can be carried out while still providing
sufficient reaction products for subsequent analysis of the
methylation state of the nucleic acid sample.
[0073] As disclosed herein, the invention provides methods for
conveniently treating nucleic acids. The methods can be used for
the analysis of the methylation state of a nucleic acid population
as a measure of the state of a cell, tissue or organism, as
disclosed herein. The methods of the invention provide several
advantages over methods previously used for treating nucleic acids.
One advantage is that the method of the invention allows omission
of the chromatography step that is traditionally used to desalt the
nucleic acid sample after sulphonation (Clark et al., 1994 Nucleic
Acids Res. 22:2990-2997). The chromatography step leads to loss of
the sulphonated nucleic acid sample, which can be particularly
problematic when working with small amounts of starting
material.
[0074] Another advantage of the invention is that the desalting
step is carried out in a highly efficient manner by diluting the
salt concentration and precipitating the nucleic acids. The
dilution step reduces the salt concentration below an amount that,
when the nucleic acid is precipitated, does not interfere with
subsequent steps such as desulphonation. The precipitation step is
highly efficient and can optionally include carriers that increase
the efficiency of nucleic acid precipitation. Thus, the methods of
the invention minimize loss and increase recovery of nucleic acid
samples. Accordingly, the methods of the invention provide the
additional advantage of allowing even smaller amounts of starting
material to be used and efficiently characterized with respect to
methylation. The invention provides methods that improve upon the
method of Clark et al., 1994 Nucleic Acids Res. 22:2990-2997, by
substituting the use of a cumbersome and inefficient chromatography
separation method with a simple dilution and precipitation method
in the step of removing any unwanted reagents or diluents from the
nucleic acids.
[0075] Further, the use of a buffer solution at slightly alkaline
pH can be used to decrease the likelihood that the nucleic acid of
interest becomes substantially fragmented. Increasing the pH of the
buffered solution to much above pH 12.5 has been demonstrated to
lead to very substantial fragmentation of high molecular weight
nucleic acids. Therefore, when it is desired to minimize such
fragmentation, an alkaline pH below about pH 11 is generally
used.
[0076] Yet another advantage of the invention is that the reactions
can be carried out in a single tube or vessel for each sample, thus
minimizing sample loss and allowing the processing of numerous
samples. A further advantage of the method of the invention
compared to previous methods is that the nucleic acids, once
sulphonated, can be resuspended in a buffer having a basic pH to
carry out the desulphonation step rather than requiring the
addition of strong base and the subsequent removal of salts, as in
the method described by Clark et al, 1994.
[0077] Still another advantage is that the methods of the invention
allow the optional digestion with restriction enzymes prior to
treatment. The traditional bisulphite treatment method generally
includes an initial digestion step with a restriction enzyme for
successful treatment and amplification and is therefore not
applicable to long distance PCR reactions. However, the methods of
the invention do not require pre-digestion with restriction enzymes
prior to the sulphonation reaction, again allowing fewer
manipulations as well as the option of performing PCR on longer
fragments.
[0078] The methods of the invention can be used to characterize the
methylation state of a cell, tissue or organism. The methods of the
invention can also be used in conjunction with genomic sequencing
methods such as those described by Frommer et al., Proc. Natl.
Acad. Sci. USA 89:1827-1831 (1992), which is incorporated herein by
reference.
[0079] The invention additionally provides a method of determining
the methylation state of a sample. The method can be carried out on
a sample using the method of the invention for treatment of nucleic
acids, that is, the HGS method. The method for determining the
methylation state of a sample can be carried out in parallel with a
test sample and a control sample so that the methylation state of
the sample can be compared and determined relative to a reference
sample. For example, the samples can be compared to determine
whether there is an increase or decrease of methylation in general
or at particular sites. Such a determination can be used to
diagnose and/or determine the prognosis of a disease, as discussed
herein. The method can further include reporting of the methylation
state of a sample, for example, in a diagnostic application.
[0080] The methods according to the present invention are
particularly suitable for use in kits. Such kits typically contain
reagents and instructions to carry out the invention. By providing
suitable kits, it is possible to allow end users to carry out work
on methylated nucleic acid with reproducible and consistent
results.
[0081] It is understood that the components of the method of the
invention can be provided in the form of a kit. The kit can contain
appropriate chemical reagents, reaction tubes and instructions for
carrying out the method of the invention.
EXAMPLES
Methods and Reagents
[0082] Chemicals were obtained as follows: Agarose from BioRad
(Hercules Calif.; certified molecular biology grade #161-3101);
Acetic acid, glacial, from BDH (Kylsyth, Australia; AnalaR
100015N); ethylenediamine tetraacetic acid (EDTA) from BDH (AnalaR
10093.5V); Ethanol from Aldrich (St. Louis Mo.; 200 proof E702-3);
Isopropanol from Sigma (St. Louis Mo.; 99%+Sigma I-9516); Mineral
oil from Sigma (M-5904); Sodium acetate solution 3M from Sigma
(S-7899); Sodium chloride from Sigma (ACS reagent S9888); and
Sodium hydroxide from BDH (AnalaR #10252.4X).
[0083] Enzymes/Reagents were obtained as follows: EcoR1 from Roche
(Indianapolis Ind.; #87930626, 10 units/.mu.l); HindIII from
Biolabs (Beverly Mass.; #R01045, 10 units/.mu.l); PCR master mix
from Promega (Madison Wis; #M7505); and DNA markers from Sigma
(Direct load PCR low ladder 100-1000 bp, Sigma D-3687 and 100-10
Kb, Sigma D-7058).
[0084] Solutions were as follows: (1) 10 mM Tris/0.1M EDTA, pH
7.0-12.5; (2) 3M NaOH (6 g in 50 ml water; BDH AnalaR #10252.4X);
(3) 2M Metabisulphite (7.6 g in 20 ml water with 416 .mu.l 10 N
NaOH (BDH AnalaR #10356.4D); (4) 10 mM Quinol (0.055 g in 50 ml
water; BDH AnalaR #103122E); (5) 50.times.TAE gel electrophoresis
buffer (242 g Trizma base, 57.1 ml glacial acetic acid, 37.2 g EDTA
and water to 1l); and (6) 5.times. Agarose gel loading buffer (1 ml
1% Bromophenol blue (Sigma B6131), 1 ml Xylene Cyanol (Sigma
X-4126), 3.2 ml Glycerol (Sigma G6279), 8 .mu.l 1 0.5M EDTA pH 8.0,
200 .mu.l 50X TAE buffer and water to 10 ml).
Tissues and Cell Lines
[0085] Tissues and cell lines were obtained as follows: HeLa
(cervical cancer cell line, ATCC CCL-2); LNCaP (prostate cancer
cell line, ATCC #CRL-10995); HepG2 (liver cancer cell line, ATCC
#HB-8065); and MCF-7 (breast cancer cell line, ATCC #HTB-22) were
obtained from American Type Culture Collection.
[0086] For preparation of T-medium for growth of LNCaP Cells,
reagents were obtained from Gibco/BRL or Invitrogen, except as
indicated, as follows: DMEM powder 10.times.sachets (10.times.1 l;
#31600-034); F-12K Nutrient mixture, Kaighn's Modifn. (500 ml;
#21127-022); L-Glutamine, 200 mM (100 ml; #25030-081);
Penicillin/Streptomycin 5000 U/ml, 5000 .mu.g/ml (100 ml #15070-063
Thermo Trace); Foetal Bovine serum (500 ml; #15-010-0500V Sigma);
Insulin (Bovine pancreas) (100 mg; #11882); Transferrin (Human) (10
mg; # T5391); d-Biotin (500 mg; #B4639); Adenine (5 g; # A3159); T3
(#T6397 or #T5516).
[0087] T-media (500 ml) was prepared as follows: DMEM stock
solution was prepared by adding 3.7 g Sodium bicarbonate per liter
and adkjusting the pH to between 7.2-7.4. To 400 ml of DMEM stock
solution, the following reagents were added: 100 ml of F-12K; 250
.mu.l of insulin (10 mg/ml); 1.0 ml T3 (500.times.;
Tri-iodothyronine; 6.825 ng/ml); 1.0 ml transferrin (500.times.;
2.5 mg/ml); 1.0 ml Biotin (500.times.; 0.122 mg/ml); 4.0 ml Adenine
(125.times.; 3.125 mg/ml); 5.5 ml Penicillin/Streptomycin
(100.times.; 5000 .mu.g/ml); and 5.5 ml Glutamine (100.times.; 200
mM). After sterile filtration, 50 ml of Foetal Bovine Serum was
added to give 10%.
[0088] Table 1 sets out the cell lines and growing conditions used
in the experiments outlined below. TABLE-US-00001 Name Cell Type
Growing Conditions BL13 Bladder Cancer RPM1 + 10% HI FCS Split 1:3,
2x week DU145 Prostate Cancer RPM1 + 10% HI FCS + 2 mM
(unmethylated) Glutamine Split 1:6, 2x week HeLa Cervical Carcinoma
RPM1 + 10% HI FCS for initial rapid growth then DMEM + 10% HI FCS
for slower growth. Split 1:10, 2x week HepG2 Liver DMEM (high
glucose 4.5 g/L) + 10% Carcinoma HI FCS + 2 mM Glutamine. Split 1:4
2x week LNCAP Prostate Cancer DMEM (low glucose) + 10% HI
(Methylated) FCS + 2 mM Glutamine + Lots of other nutrients, see
LNCaP growth method sheet. MCF7 Breast Cancer RPM1 + 10% HI FCS
Split 1:6, 2x week
Purification of T-cells and CD34+ Cells from Whole Blood
[0089] Samples were obtained from a patient undergoing
leukapheresis at the Royal North Shore Hospital, Sydney. Samples
were obtained with prior Ethics Committee approval. White blood
cells were concentrated using Ficoll Paque plus (Amersham
Biosciences #17-1440-03; Piscataway N.J.) according to the
manufacturers instructions. T-cells and CD34+ cells were isolated
from the white cell population using CELLection CD2 Dynabeads
(Dynal #116.03; Lake Success N.Y.) and Dynal CD34 Progenitor Cell
selection system (Dynal #113.01) respectively according to the
manufactures instructions.
[0090] The following equipment was used: the PCR machine was
ThermalHybaid PX2 (Sydney, Australia) the Gel Documentation System
was a Kodak UVItec EDAS 290 (Rochester N.Y.), and the microfuge was
an Eppendorf 5415-D (Brinkman Instruments; Westbury N.Y.).
DNA Amplification
[0091] PCR amplifications were performed in 25 .mu.l reaction
mixtures containing 2 .mu.l of bisulphite-treated genomic DNA,
using the Promega PCR master mix, 6 ng/.mu.l of each of the
primers. The strand-specific nested primers used for amplification
of GSTP1 from bisulphite-treated DNA are GST-9 (967-993)
TTTGTTGTTTGTTT ATTTTTTAGGTTT (SEQ ID NO:1); (F) GST-10 (1307-1332)
AACCTAATACTACCAATTAACCCCAT (SEQ ID NO:2) (R); GST-11 (999-1027)
GGGATTTGGGAAAGAGGGAAAGGTTTTTT (SEQ ID NO:3) (F); GST-12 (1281-1306)
ACTAAAAACTCTAAAAACCCCATCCC (SEQ ID NO:4) (R). The location of the
primers is indicted according to the GSTP1 sequence (Accession
number: M24485; GenBank citation Morrow et al., Gene 75:3-11
(1989)).
RNA Purification Du145 cells were grown to 90% confluence in T75
tissue culture flasks under the conditions described above. The
media was discarded and 3 ml of Trizol (Invitrogen Cat# 15596-026)
added and the samples processed as follows:
[0092] I. Samples were mixed well and left at room temperature for
5 minutes to dissociate nucleoprotein complexes. [0093] II. The
samples were then spun at 12,000.times.g for 10 minutes at
4.degree. C. to remove high molecular weight DNA and other
contaminants. [0094] III. The supernatant was removed into a clean
tube and 100 .mu.l of 100% chloroform added and the samples were
mixed vigourously by hand for 15 seconds then incubated at room
temperature for 2-3 minutes. [0095] IV. The samples were then spun
at 12,000.times.g for 10 minutes at 4.degree. C. to separate the
phases. [0096] V. The upper aqueous phase was removed into a clean
tube ensuring the pipette tip stayed away from the interface and 1
.mu.l of 20 mg/ml glycogen added and the samples vortexed. [0097]
VI. An equal volume of 100% (0.25 ml) was added the tubes vortexed
then left at room temperature for 10 minutes. [0098] VII. The
samples were then spun at 12,000.times.g for 10 minutes at
4.degree. C. to pellet the RNA. [0099] VIII. The supernatant was
removed and the pellet washed with 0.75 ml of 80% ethanol to
removed inhibitors of the cDNA synthesis reaction, vortexed
briefly, then spun at 7,500.times.g for 5 minutes at 4.degree. C.
to pellet the RNA. [0100] IX. Step VIII was repeated a further
time. [0101] X. The pellet was then spun in a microfuge for 10
seconds, the residual ethanol removed and the pellet immediately
resuspended in 25 .mu.l of RNase free water. NB if the pellet dries
out then it is very difficult to resuspend the RNA and the 260/280
ratio will be less than 1.6. [0102] XI. The OD 260/280/310 is then
recorded. [0103] XII. Purified RNA was then stored at -70.degree.
C. until required cDNA Synthesis
[0104] cDNA synthesis was performed using superscript III
(Invitrogen Cat# 18080-044) with 100 ng random heamers (invitrogen
Cat# 48910-011) as recommended by the manufacturers
instructions.
RNA Amplification
[0105] PCR amplifications were performed in 25 .mu.l reaction
mixtures containing 2 .mu.l of bisulphite-treated reverse
transcribed genomic RNA, using the Promega PCR master mix, 6
ng/.mu.l of each of the primers. The strand-specific primers used
for amplification of Actin from bisulphite-treated RNA were
ActinBS-3A (2076-2097) TTAATATTTTAGTTATGTATGTTGT SEQ ID NO:5);
ActinBS-4 (2720-2744). CTTCATTATACTAAATACCAAA (SEQ ID NO:6).
[0106] Control primers against wild type actin RNA were also
included to ensure that the RNA amplified originated from
bisulphite converted RNA and not that of wild type RNA. The
following wild type primers were synthesised Actin wild-type 3A
(2076-2097) TCAACACCCCAGCCATGTACGTTGC (SEQ ID NO:7), Actin
wild-type 4 (2720-2744) GATCTTCATTGTGCTGGGTGCC (SEQ ID NO:8). The
location of the primers is indicted according to the human
beta-actin gene sequence (Accession number: M10277).
[0107] Nucleic Acid Separation 1% or 2% agarose gels were prepared
in 1% TAE containing 1 drop ethidium bromide (CLP #5450) per 50 ml
of agarose. The DNA or RNA sample of interest (genomic or PCR
derived) was mixed with 1/5.sup.th volume 5.times. agarose loading
buffer and electrophoresed at 125 mA in .times.1 TAE using a
submarine horizontal electrophoresis tank.
[0108] Traditional Bisulphite Treatment of DNA (Clark et al.,
(1994) Nucleic Acids Res. 22:2990-2997, which is incorporated
herein by reference) (prior art method that results extremely in
poor yields of DNA)
[0109] Genomic DNA (2 .mu.g) was digested with Eco R1 for 60
minutes at least in a final volume of 20 .mu.l. To this digest, 2.2
.mu.l of 3M NaOH (6 g NaOH/50 ml water, made fresh) were added and
incubated at 37.degree. C. for 15 minutes. A 208 .mu.l volume of 2M
Metabisulphite (7.6 g metabisulphite/20 ml water and 416 .mu.l 10M
NaOH to pH 5.0) was added followed by 12 .mu.l of 10 mM quinone
(0.55 g hydroquinone gives 100 mM, dilute 1/10). The reaction
mixture was overlaid with 200 .mu.l of mineral oil and incubated at
50-55.degree. C. overnight. At the end of the incubation, the
mineral oil was removed and 1 .mu.g yeast tRNA (Sigma R-8508) was
added.
[0110] DNA desalting was carried out using the Wizard DNA clean up
system (Promega #A7280) according to the manufactures instructions.
Briefly, 1 ml of resin was added to the sample and the sample
vortexed. The sample was applied to a column attached to a 2.5 ml
syringe and pushed through the syringe gently. The column was
washed with 2 ml of 80% isopropanol and then spun for 20 seconds at
14,000 rpm in a microfuge. Fifty .mu.l of water was applied to the
column and the sample left for 1 minute at room temperature. The
column material was applied to a clean 1.5 ml centrifuge tube and
was spun for 20 seconds at 14,000 rpm in a microfuge. The DNA was
recovered in the eluted volume, ready for de-sulphonation.
[0111] To remove the sulphate groups from uracil, 5.5 .mu.l of 3M
NaOH were added to the eluted DNA and the mixture was incubated at
37.degree. C. for 15 minutes. A 33.5 .mu.l volume of NH.sub.4OAC
(pH 7.0) was added to neutralize the alkali. A 330 .mu.l of 100%
ethanol was added, and the reaction mixture was incubated at
-20.degree. C. for 60 minutes. The sample was spun 15 minutes at
14,000 rpm and the ethanol was discarded. The pellet was air dried
and resuspended in 10 .mu.l T/E (pH 8.0).
HGS Bisulphite Treatment of Nucleic Acid
[0112] An exemplary protocol demonstrating the effectiveness of the
bisulphite treatment according to the present invention is set out
below. The protocol successfully resulted in retaining
substantially all nucleic acid treated. This method of the
invention is also referred to herein as the HGS bisulphite method.
It will be appreciated that the volumes or amounts of sample or
reagents can be varied.
DNA Denaturation
[0113] To 2 .mu.g of DNA, which can be pre-digested with suitable
restriction enzymes if so desired, 2 .mu.l (1/10 volume) of 3 M
NaOH (6 g in 50 ml water, freshly made) was added in a final volume
of 20 .mu.l. This step denatures the double stranded DNA molecules
into a single stranded form, since the bisulphite reagent
preferably reacts with single stranded molecules. The mixture was
incubated at 37.degree. C. for 15 minutes. Incubation at
temperatures above room temperature can be used to improve the
efficiency of denaturation.
RNA Denaturation
[0114] Two .mu.g of RNA was resuspended in a total volume of 20
.mu.l containing 1 .mu.l of RNase inhibitor (RNaseOUT Invitrogen
Cat# 10777-019 40U/.mu.l). This solution was then heated at
50.degree. C for 2 minutes then snap chilled on ice (optional).
This step denatures the RNA molecules into a form essentially free
of secondary structure, as the bisulphite reagent preferably reacts
with single stranded molecules.
Bisulphite Treatment of DNA
[0115] After the incubation, 208 .mu.l 2 M Sodium Metabisulphite
(7.6 g in 20 ml water with 416 ml 10 N NaOH; BDH AnalaR #10356.4D;
freshly made) and 12 .mu.l of 10 mM Quinol (0.055 g in 50 ml water,
BDH AnalR #103122E; freshly made) were added in succession. Quinol
is a reducing agent and helps to reduce oxidation of the reagents.
Other reducing agents can also be used, for example, dithiothreitol
(DTT), mercaptoethanol, quinone (hydroquinone), or other suitable
reducing agents. The sample was overlaid with 200 .mu.l of mineral
oil. The overlaying of mineral oil prevents evaporation and
oxidation of the reagents but is not essential. The sample was then
incubated overnight at 550.degree. C.
[0116] Alternatively the samples can be cycled in a thermal cycler
as follows: incubate for about 4 hours or overnight as follows:
Step 1, 55.degree. C./2 hr cycled in PCR machine; Step 2,
95.degree. C./2 min. Step 1 can be performed at any temperature
from about 37.degree. C. to about 90.degree. C. and can vary in
length from 5 minutes to 8 hours. Step 2 can be performed at any
temperature from about 70.degree. C. to about 99.degree. C. and can
vary in length from about 1 second to 60 minutes, or longer.
[0117] After the treatment with Sodium Metabisulphite, the oil was
removed, and 1 .mu.l tRNA (20 mg/ml) or 2 .mu.l glycogen were added
if the DNA concentration was low. These additives are optional and
can be used to improve the yield of DNA obtained by
co-precipitating with the target DNA especially when the DNA is
present at low concentrations. The use of additives as carrier for
more efficient precipitation of nucleic acids is generally desired
when the amount nucleic acid is <0.5 .mu.l.
[0118] An isopropanol cleanup treatment was performed as follows:
800 .mu.l of water were added to the sample, mixed and then 1 ml
isopropanol was added. The water or buffer reduces the
concentration of the bisulphite salt in the reaction vessel to a
level at which the salt will not precipitate along with the target
nucleic acid of interest. The dilution is generally about 1/4 to
1/1000 so long as the salt concentration is diluted below a desired
range, as disclosed herein.
[0119] The sample was mixed again and left at 4.degree. C. for a
minimum of 5 minutes. The sample was spun in a microfuge for 10-15
minutes and the pellet was washed 2.times. with 80% ETOH, vortexing
each time. This washing treatment removes any residual salts that
precipitated with the nucleic acids.
[0120] The pellet was allowed to dry and then resuspended in a
suitable volume of T/E (10 mM Tris/0.1 mM EDTA) pH 7.0-12.5 such as
50 .mu.l. Buffer at pH 10.5 has been found to be particularly
effective. The sample was incubated at 37.degree. C. to 95.degree.
C. for 1 min to 96 hr, as needed to suspend the nucleic acids.
[0121] The method described above can be preceded by digestion with
one or more restriction enzymes. Two independent restriction enzyme
digests are set up of the same sample of DNA as described below.
The enzymes selected for digestion are dependent 30 upon the
sequence to be amplified. For example, digest 2 .mu.l genomic DNA
with EcoRI in a 20 .mu.l volume for 1 hr/at 37.degree. C. This step
is used to digest the genomic DNA into smaller fragments which are
more amenable to bisulphite conversion than genomic DNA. Sonication
or physical forces can also be used to shear the DNA into smaller
sized fragments. The intensity of sonication and the length of
sonication is selected based on the desired size of DNA fragments.
A separate digestion reaction is carried out, for example, by
digesting 2 .mu.g genomic DNA with HindIII as described above.
These or other suitable restriction enzymes can be selected for
pretreatment digestion. The digested DNA is treated with
metabisulfite as described above.
Bisulphite Treatment of RNA
[0122] After the incubation, 208 .mu.l 2 M Sodium Metabisulphite
(7.6 g in 20 ml water with 416 ml 10 N NaOH; BDH AnalaR #10356.4D;
freshly made) was added. The sample was overlaid with 200 .mu.l of
mineral oil. The overlaying of mineral oil prevents evaporation and
oxidation of the reagents but is not essential. The sample was then
incubated 3 hours to overnight at 37.degree. C. to 55.degree. C.
Alternatively the samples can be cycled in a thermal cycler as
follows: incubate for about 4 hours or overnight as follows: Step
1, 55.degree. C./2 hr cycled in PCR machine; Step 2, 70.degree.
C./30 seconds. Step 1 can be performed at any temperature from
about 37.degree. C. to about 90.degree. C. and can vary in length
from 5 minutes to 8 hours. Step 2 can be performed at any
temperature from about 60.degree. C. to about 99.degree. C. and can
vary in length from about 1 second to 60 minutes, or longer.
[0123] After the treatment with Sodium Metabisulphite, the oil was
removed, and 1 .mu.l glycogen was added if the RNA concentration
was low. This additive is optional and can be used to improve the
yield of RNA obtained by co-precitpitating with the target RNA
especially when the RNA is present at low concentrations. The use
of additives as carrier for more efficient precipitation of nucleic
acids is generally desired when the amount nucleic acid is <0.5
.mu.g.
[0124] An isopropanol cleanup treatment was performed as follows:
800 .mu.l of water were added to the sample, mixed and then 1 ml
isopropanol was added. The water or buffer reduces the
concentration of the bisulphite salt in the reaction vessel to a
level at which the salt will not precipitate along with the target
nucleic acid of interest. The dilution is generally about 1/4 to
1/1000 so long as the salt concentration is diluted below a desired
range, as disclosed herein.
[0125] The sample was mixed again and left at room temperature for
15 minutes. The sample was spun in a microfuge for 10-15 minutes
and the pellet was washed 2.times. with 80% ETOH, vortexing between
washes. This washing treatment removes any residual salts that
precipitated with the nucleic acids.
[0126] The pellet was allowed to dry and then resuspended in a
suitable volume of T/E (10 mM Tris/0.1 mM EDTA) pH 7.0-12.5 such as
50 .quadrature.l. Buffer at pH 10.5 has been found to be
particularly effective. The sample was incubated at 37.degree. C.
to 95.degree. C. for 1 min to 96 hr, as needed to suspend the
nucleic acids.
[0127] Sonication or physical forces can also be used to shear the
RNA into smaller sized fragments. The intensity of sonication and
the length of sonication is selected based on the desired size of
RNA fragments.
RESULTS
DNA Analysis of LNCaP Cells and Sensitivity of PCR
Amplification
[0128] Cultures of LNCaP cells were grown under standard conditions
to 90% confluence. Cells were trypsinised, washed, then counted
using a haemocytometer. Cells were then diluted to contain the
approximate number of cells as indicated in Table 2. The cells were
then lysed using MasterPure DNA Purification kit (Epicentre
#MCD85201; Madison Wis.) as described by the manufacturers
instructions and the DNA then modified using the two sulphonation
methods described above.
[0129] After accurate determination of cell numbers, cultures were
split in duplicate into 1.5 ml eppendorf centrifuge tubes at the
following cell numbers 100, 1000, 10000 and 100000 in 25 .mu.l of
T/E pH 8.0. Cell lysis was then performed on the cells as described
by the manufacture's instructions MasterPure DNA Purification kit
(Epicentre #MCD85201) as described by the manufacturers
instructions.
[0130] DNA was resuspended in 10 .mu.l of T/E pH 8.0. DNA was then
digested with 1 unit of EcoR1 (Roche #87930626 10 units/.mu.l)
according to the manufacturers instructions for 1 hour at
37.degree. C. in a final volume of 20 .mu.l.
[0131] Traditional bisulphite treatment of DNA (Clark et al 1994)
was performed on one set of duplicates while the HGS bisulphite
treatment of DNA was performed on the other set. After treatment
DNA was resuspended in 5 .mu.l of T/E pH 8.0.
[0132] PCR amplification was performed on 1 .mu.l of treated DNA,
1/5.sup.th volume of final resuspended sample volume, as follows.
PCR amplifications were performed in 25 .mu.l reaction mixtures
containing 1 .mu.l of bisulphite-treated genomic DNA, using the
Promega PCR master mix, 6 ng/.mu.l of each of the primers. The
strand-specific nested primers used for amplification of GSTP1 from
bisulphite-treated DNA are GST-9 (967-993) TTTGTTGTTTGTTTAGGTTT
(SEQ ID NO:1) (F) GST-10 (1307-1332) AACCTAATACTACCAATTAACCCCAT
(SEQ ID NO:2) 1.sup.st round amplification conditions.
[0133] One .mu.l of 1.sup.st round amplification was transferred to
the second round amplification reaction mixtures containing
primers(R) GST-11 (999-1027) GGGATTTGGGAAAGAGGGAAAGGTTTTTT (SEQ ID
NO:3) (F) GST-12 (1281-1306) ACTAAAAACTCTAAAAACCCCATCCC (SEQ ID
NO:4) (R). The location of the primers is indicted according to the
GSTP1 sequence (Accession number: M24485). Samples of PCR products
were amplified in a ThermoHybaid PX2 thermal cycler under the
conditions described in Clark et al.
[0134] Agarose gels (2%) were prepared in 1% TAE containing 1 drop
ethidium bromide (CLP #5450) per 50 ml of agarose. Five .mu.l of
the PCR derived product was mixed with 1 .mu.l of 5.times. agarose
loading buffer and electrophoresed at 125 mA in .times.1 TAE using
a submarine horizontal electrophoresis tank. Markers were the low
100-1000 bp type. Gels were visualised under UV irradiation using
the Kodak UVIdoc EDAS 290 system.
[0135] Table 2 shows a comparison of the sensitivity of PCR
amplification between the HGS method of the invention and the
traditional method of Clark et al. TABLE-US-00002 TABLE 2
Sensitivity of PCR-based amplification of the GSTP1 Gene using the
HGS method versus traditional bisulphite amplification procedures
(Clark et al, 1994) Sensitivity of PCR Amplification Method 20,000
2,000 200 20 HGS Yes Yes Yes Yes traditional Yes Yes No No
Effect of pH on Degradation of Bisulphite Treated Genomic DNA
[0136] Two .mu.g of LNCaP DNA was digested with 2 units of EcoR1
(Roche #87930626 10 units/.mu.l) according to the manufacturers
instructions for 1 hour at 37.degree. C. in a final volume of 20
.mu.l. Eight individual reactions were prepared.
[0137] HGS bisulphite treatment of DNA was performed on each of the
digests. After treatment, DNA from each individual treatment was
resuspended in 20 .mu.l of T/E at either pH 7.0, 8.0, 8.5, 9.0,
9.5, 10.0, 10.5 and 12.5.
[0138] The DNA was then incubated using the following methods.
[0139] Treatment 1. HGS bisulphite treated genomic DNA was
resuspended in buffer solution pH 10.5 and left at 37.degree. C.
for 30 minutes then PCR amplified. [0140] Treatment 2. HGS
bisulphite treated genomic DNA was resuspended in buffer solution
pH 10.5 and left at 37.degree. C. for 120 minutes then PCR
amplified. [0141] Treatment 3. HGS bisulphite treated genomic DNA
was resuspended in buffer solution pH 10.5 and left at 55.degree.
C. for 30 minutes then PCR amplified.
[0142] A 1% agarose gel was prepared in 1% TAE containing 1 drop
ethidium bromide (CLP #5450) per 50 ml of agarose. Ten .mu.l of the
genomic DNA sample was mixed with 1/5.sup.th volume 5.times.
agarose loading buffer (2 .mu.l) and electrophoresed at 125 mA in
.times.1 TAE using a submarine horizontal electrophoresis tank.
Markers were the 100-10,000 range. The gel was visualised and
photographed under UV irradiation using the Kodak UVIdoc EDAS 290
system.
PCR Analysis on the Samples
[0143] PCR amplification was performed on 1 .mu.l of bisulphite
treated DNA resuspended sample DNA as follows.
[0144] PCR amplifications were performed in 25 .mu.l reaction
mixtures containing 1 .mu.l of bisulphite-treated genomic DNA,
using the Promega PCR master mix, 6 ng/.mu.l of each of the
primers. The strand-specific nested primers used for amplification
of GSTP1 from bisulphite-treated DNA are GST-9 (967-993)
TTTGTTGTTTGTTTATTTTTTAGGTTT (F) GST-10 (1307-1332)
AACCTAATACTACCAATTAACCCCAT 1.sup.st round amplification
conditions.
[0145] One .mu.l of 1.sup.st round amplification was transferred to
the second round amplification reaction mixtures containing primers
(R) GST-11 (999-1027) GGGATTTGGGAAAGAGGGAAAGGTTTTTT (SEQ ID NO:3);
(F) GST-12 (1281-1306) ACTAAAAACTCTAAAAACCCCATCCC (R) (SEQ ID
NO:4). The location of the primers is indicted according to the
GSTP1 sequence (Accession number: M24485). Samples PCR products
were amplified in a ThermoHybaid PX2 thermal cycler under the
conditions described in Clark et al 1994.
[0146] Agarose gels (2%) were prepared in 1% TAE containing 1 drop
ethidium bromide (CLP #5450) per 50 ml of agarose. Five .mu.l of
the PCR derived product was mixed with 1 .mu.l of 5.times. agarose
loading buffer and electrophoresed at 125 mA in 1.times.TAE using a
submarine horizontal electrophoresis tank. Markers were the low
100-1000 bp type. Gels were visualised under UV irradiation using
the Kodak UVIdoc EDAS 290 system.
[0147] The results are summarized in Table 3. The first point of
the results of Table 3 is o demonstrate that when the pH of the
bisulphite treated genomic DNA solution is low, then no significant
amplification can be detected by standard PCR methods. This is
probably due to incomplete de-sulphonation of the bisulphite
treated genomic DNA.
[0148] The results in Table 3 demonstrate that there is dynamic
equilibrium between pH and temperature with regard to the rate of
de-sulphonation of the bisulphite treated genomic DNA. If the
bisulphite treated genomic DNA is left in low pH solutions, then
the rate of de-sulphonation is very slow but can be improved by
increasing the temperature of the solution. For example, it may be
possible to have the bisulphite treated genomic DNA at pH 7.0, heat
it at 72.degree. C., leave it for 48 hours, and then achieve
complete de-sulphonation. Likewise, at pH 10.5 the reaction may be
finished in 5 minutes at 72.degree. C. Thus, a range of
temperatures from room temperature to about 95.degree. C. would be
suitable for the present invention. pH ranges from 7.0 to 12.5 and
incubation times from about 1 minute to about 96 hours would be
suitable. It will be appreciated that various possible combinations
of pH, time and temperature would be suitable.
[0149] In addition, if the samples were treated with the
conventional method, then there would be a large loss of DNA when
the bisulphite treated genomic DNA is passed down a size exclusion
chromatography column to desalt the solution. It is very likely
that at least 50% of the bisulphite treated genomic DNA, if not
more, is lost because the conventional columns that are used in the
prior art are not designed for single stranded DNA material and
there is a large loss. Using the HGS procedure without column
purification, the loss by the HGS procedure is miniscule.
TABLE-US-00003 TABLE 3 Effect of pH on the degradation of
bisulphite treated genomic DNA using the HGS methodology pH of the
buffered DNA solution 7.0 8.0 8.5 9.0 9.5 10.0 10.5 12.5 High
molecular No No No No No No No Yes weight DNA Degraded PCR Product
pH of the buffered DNA solution Generation 7.0 8.0 8.5 9.0 9.5 10.0
10.5 12.5 PCR product No No No No No No No Yes Treatment 1 PCR
product ND ND ND ND ND Faint Yes ND Treatment 2 PCR product ND ND
ND ND ND ND Yes ND Treatment 3 Treatment 1. HGS bisulphite treated
genomic DNA was resuspended in buffer solution pH 10.5 and left at
37.degree. C. for 30 minutes then PCR amplified. Treatment 2. HGS
bisulphite treated genomic DNA was resuspended in buffer solution
pH 10.5 and left at 37.degree. C. for 120 minutes then PCR
amplified. Treatment 3. HGS bisulphite treated genomic DNA was
resuspended in buffer solution pH 10.5 and left at 55.degree. C.
for 30 minutes then PCR amplified.
Bisulphite Treatment of Various Cell Lines and Tissues
[0150] One .mu.g of DNA from the following cell lines and tissue
samples were digested with 2 units of EcoR1 (Roche #87930626 10
units/.mu.l) in duplicate according to the manufacturers
instructions for 1 hour at 37.degree. C. in a final volume of 20
.mu.l: LNCaP Prostate cancer cell line DNA, MCF-7 Breast cancer
cell line DNA, BL-13 Bladder cancer cell line DNA, HepG2 Liver
cancer cell line DNA, HeLa cervical cancer cell line DNA, T-cells
from purified Patient # 1, and CD34+ cells purified from Patient #
1
[0151] HGS bisulphite treatment of DNA was performed on one set of
the digests. After treatment, DNA from each individual sample was
resuspended in 20 .mu.l of T/E at either pH 10.5 and incubated at
55.degree. C. for 2 hours. Traditional bisulphite treatment of DNA
(Clark et al 1994) was performed on the other set in which after
the DNA was modified it was resuspended in 20 .mu.l of T/E pH
8.0.
PCR Analysis on the Samples
[0152] PCR amplification was performed on 1 .mu.l of both the
traditional and HGS bisulphite treated DNA. Six individual genomic
loci were analysed for each sample to determine the genomic
coverage represented by the HGS and the traditional bisulphite
modification methods.
[0153] PCR amplifications were performed in 25 .mu.l reaction
mixtures containing 1 .mu.l of bisulphite-treated genomic DNA,
using the Promega PCR master mix and 6 ng/.mu.l of each of the
1.sup.st round gene specific primers. One .mu.l of 1.sup.st round
amplification was transferred to the second round amplification
reaction mixtures containing 2.sup.nd round gene specific primers.
PCR products were amplified in a ThermoHybaid PX2 thermal cycler
under the conditions described in Clark et al 1994.
[0154] Two % agarose gels were prepared in 1% TAE containing 1 drop
ethidium bromide (CLP #5450) per 50 ml of agarose. A 5 .mu.l
aliquot of the PCR derived product was mixed with 1 .mu.l of
5.times. agarose loading buffer and electrophoresed at 125 mA in
.times.1 TAE using a submarine horizontal electrophoresis tank.
Markers were the low 100-1000 bp type. Gels were visualised under
UV irradiation using the Kodak UVIdoc EDAS 290 system.
[0155] Genomic DNA treated with the HGS bisulphite method was
amplified using conventional PCR technologies with primers designed
to detect the GSTP1 gene. The results of the comparison between the
prior art method and the method according to the present invention
are set out in Table 4. TABLE-US-00004 TABLE 4 Whole Genome
Amplification efficiency of HGS method versus traditional
bisulphite amplification Procedures (Clark et al, 1994) HGS method
amplification Traditional Bisulphite of Gene 1-6 amplification of
Gene 1-6 Tissue 1 2 3 4 5 6 1 2 3 4 5 6 a yes yes yes yes yes yes
no no no no no no b yes yes yes yes yes yes no yes yes no no no c
yes yes yes yes yes yes yes yes yes yes no yes d yes yes yes yes
yes yes no yes yes no no no e yes yes yes yes yes yes yes yes no no
yes yes f yes yes yes yes yes yes yes yes no no no no Tissue
samples of Table 4 are as follows: a LNCaP Prostate cancer cell
line DNA b MCF-7 Breast cancer cell line DNA c HepG2 Liver cancer
cell line DNA d HeLa cervical cancer cell line DNA e T-cells from
purified Patient # 1 f CD34+ cells purified from Patient # 1
[0156] FIG. 1 shows comparison of recovery of bisulphite-treated
DNA from various tissue samples between the HGS bisulphite method
and traditional bisulphite method (Clark et al 1994). Well #1. DNA
extracted from 2 LNCaP cells and treated with bisulphite, Well #2.
DNA extracted from 20 LNCaP cells and treated with bisulphite, Well
#3. DNA extracted from 200 LNCaP cells and treated with bisulphite,
Well #4. DNA extracted from 2,000 LNCaP cells and treated with
bisulphite and Well#5. DNA extracted from 20,000 LNCaP cells and
treated with bisulphite
[0157] As can be seen from FIG. 1, the recovery of DNA using the
method according to the present invention is vastly superior to
that of the prior art method.
RNA Results
[0158] FIG. 2 shows results obtained using the HGS bisulphite
treatment on RNA extracted from the prostate cancer cell line Du145
compared to using the conventional bisulphite approach.
[0159] As can be seen, high molecular weight RNA was observed in
all samples treated with the HGS method at 4.degree. C., room
temperature and 55.degree. C. The 23S, 18S and 5S ribosomal RNA
bands are clearly visible and it can also be seen that there is
very little degradation of the RNA when compared to the control. In
contrast, RNA treated by the conventional method has been totally
degraded.
[0160] FIG. 3 shows a time course experiment on the stability of
the RNA using different temperature incubations. From the result it
can be seen that a small amount of degradation takes place in the
1.sup.st 30 minutes of incubation but then reaches an almost steady
state and very little is lost subsequently even after 16 hour
incubation at 55.degree. C.
[0161] FIG. 4 shows Reverse Transcriptase PCR performed on both
bisulphite converted RNA and wild type RNA. As can be seen strong
PCR amplification signals are seen in the bisulphite treated RNA at
the same size as the bands in the wild type RNA.
[0162] When bisulphite treated RNA was used as a template for
RT-PCR using wild type primers or when wild type RNA was used as a
template for RT-PCR with bisulphite converted primers no bands were
detected. This indicates that the bisulphite reaction has converted
with near 100% efficiency the wild type RNA into converted RNA.
[0163] FIG. 5 shows confirmation that the PCR products generated in
FIG. 4 were derived from the bisulphite treated genomic RNA. The
arrow shows the splice site between exon 3 and 4 in the human
beta-actin transcript.
[0164] It will be appreciated by persons skilled in the art that
numerous variations and/or modifications may be made to the
invention as shown in the specific embodiments without departing
from the spirit or scope of the invention as broadly described. The
present embodiments are, therefore, to be considered in all
respects as illustrative and not restrictive.
Sequence CWU 1
1
8 1 27 DNA human 1 tttgttgttt gtttattttt taggttt 27 2 26 DNA Human
2 aacctaatac taccaattaa ccccat 26 3 29 DNA Human 3 gggatttggg
aaagagggaa aggtttttt 29 4 26 DNA Human 4 actaaaaact ctaaaaaccc
catccc 26 5 25 DNA Human 5 ttaatatttt agttatgtat gttgt 25 6 22 DNA
human 6 cttcattata ctaaatacca aa 22 7 25 DNA human 7 tcaacacccc
agccatgtac gttgc 25 8 22 DNA human 8 gatcttcatt gtgctgggtg cc
22
* * * * *
References