U.S. patent application number 15/406160 was filed with the patent office on 2018-03-29 for mutant reverse transcriptase.
This patent application is currently assigned to New England Biolabs, Inc.. The applicant listed for this patent is New England Biolabs, Inc.. Invention is credited to Shengxi Guan, Nicole Nichols, Jennifer Ong, Yan Xu.
Application Number | 20180087036 15/406160 |
Document ID | / |
Family ID | 58056537 |
Filed Date | 2018-03-29 |
United States Patent
Application |
20180087036 |
Kind Code |
A1 |
Xu; Yan ; et al. |
March 29, 2018 |
Mutant Reverse Transcriptase
Abstract
A mutant MMLV reverse transcriptase that may have an improvement
in one or more properties is provided. For example, the present
reverse transcriptase is believed to be more efficient relative to
other commercially available MMLV reverse transcriptase variants,
particularly for templates with a higher GC content.
Inventors: |
Xu; Yan; (Hamilton, MA)
; Ong; Jennifer; (Salem, MA) ; Guan; Shengxi;
(Stoneham, MA) ; Nichols; Nicole; (Reading,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
New England Biolabs, Inc. |
Ipswich |
MA |
US |
|
|
Assignee: |
New England Biolabs, Inc.
Ipswich
MA
|
Family ID: |
58056537 |
Appl. No.: |
15/406160 |
Filed: |
January 13, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15274622 |
Sep 23, 2016 |
9580698 |
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15406160 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C12N 15/10 20130101;
C12N 9/22 20130101; C12P 19/34 20130101; C12N 9/1276 20130101; C12Y
301/26004 20130101; C12Y 207/07049 20130101; C12Q 1/686
20130101 |
International
Class: |
C12N 9/22 20060101
C12N009/22; C12N 9/12 20060101 C12N009/12 |
Claims
1-10. (canceled)
11. A method comprising: (a) obtaining a reaction mix by combining
a primer, an RNA template and a reverse transcriptase, wherein the
reverse transcriptase comprises: at least 300 contiguous amino
acids of SEQ ID NO: 1; and (b) incubating the reaction mix to
produce cDNA copied from the RNA template.
12. The method of claim 11, wherein the reaction mix is incubated
at temperature in the range of 45-60.degree. C.
13. The method of claim 11, further comprises a template switching
oligonucleotide.
14. The method of claim 11, wherein the primer is an oligo-dT
primer.
15. The method of claim 11, wherein the primer is a random
primer.
16. The method of claim 11, wherein the primer is a gene-specific
primer.
17. The method of claim 11, wherein the reverse transcriptase
comprises an exogenous sequence-specific DNA binding domain.
18. The method of claim 11, wherein the reverse transcriptase
comprises an amino acid sequence that is at least 90% identical to
at least 300 contiguous amino acids of SEQ ID NO:2 that is
C-terminal to the at least 300 contiguous amino acids of SEQ ID
NO:1.
19. The method of claim 11, wherein the reverse transcriptase does
not have RNAseH activity.
20. The method of claim 11, wherein the reverse transcriptase has
RNAseH activity.
21. The method of claim 11, wherein the method comprises: (c)
amplifying the cDNA produced in step (b).
22. The method according to claim 11, wherein the amplification is
PCR.
23. The method of claim 11, wherein the method comprises
quantifying the cDNA produced in step (b).
24. A method comprising: (a) obtaining a reaction mix by combining
a primer, an RNA template and a reverse transcriptase, wherein the
reverse transcriptase comprises: (i) amino acids 24-335 of SEQ ID
NO: 1 and (ii) an amino acid sequence that is at least 90%
identical to amino acids 1-286 of SEQ ID NO: 1, wherein the amino
acid sequence of (i) is N-terminal to the amino acid sequence of
(ii); and (b) incubating the reaction mix to produce cDNA copied
from the RNA template.
Description
BACKGROUND
[0001] Reverse transcriptases are multi-functional enzymes with
three enzymatic activities including RNA- and DNA-dependent DNA
polymerization activity, and an RNaseH activity that catalyzes the
cleavage of RNA in RNA-DNA hybrids. Mutants of reverse
transcriptases have disabled the RNaseH moiety to prevent
unintended damage to the mRNA. These enzymes that synthesize
complementary DNA (cDNA) using mRNA as a template were first
identified in RNA viruses. Subsequently, reverse transcriptases
were isolated and purified directly from virus particles, cells or
tissues. (e.g., see Kacian et al., 1971, Biochim. Biophys. Acta 46:
365-83; Yang et al., 1972, Biochem. Biophys. Res. Comm. 47: 505-11;
Gerard et al., 1975, J. Virol. 15: 785-97; Liu et al., 1977, Arch.
Virol. 55 187-200; Kato et al., 1984, J. Virol. Methods 9: 325-39;
Luke et al., 1990, Biochem. 29: 1764-69 and Le Grice et al., 1991,
J. Virol. 65: 7004-07). More recently, mutants and fusion proteins
have been created in the quest for improved properties such as
thermostability, fidelity and activity.
[0002] Copying RNA can be inhibited by the presence of RNA
secondary structure which can stall cDNA synthesis resulting in
truncated cDNA molecules. The formation of secondary structure can
be avoided at higher temperature. While this also reduces
non-specific priming and thereby increases reverse transcriptase
fidelity, length and yield of cDNA. However, RNA integrity can be
compromised by lower enzyme activity at elevated temperatures.
Further improvements are desirable to obtain optimum performance of
the enzymes in library synthesis and NextGen sequencing.
SUMMARY
[0003] A mutant Moloney murine leukemia virus (MMLV) reverse
transcriptase that may have an improvement in one or more
properties is provided. For example, the present reverse
transcriptase is believed to be more efficient relative to other
commercially available MMLV reverse transcriptase variants,
particularly for templates with a higher GC content. In some
embodiments, use of the present MMLV reverse transcriptase may
increase the proportion of full length cDNA molecules at a
temperature that is higher than 42.degree. C. (e.g., a temperature
in the range of 45.degree. C. to 60.degree. C.). The present MMLV
reverse transcriptase has at least 7 amino acid substitutions
relative to the wild type MMLV reverse transcriptase.
[0004] This disclosure provides, among other things, a polypeptide
comprising at least 300 contiguous amino acids of SEQ ID NO:1. The
polypeptide may comprise at least amino acid residues 24-335 of SEQ
ID NO:1 and, in some embodiments may have a truncated N-terminus
relative to SEQ ID NO:1. In some embodiments, the polypeptide may
comprise the entire contiguous sequence of SEQ ID NO:1.
[0005] In some embodiments, the polypeptide may additionally
comprise an amino acid sequence that is at least 90% identical to
at least 286 contiguous amino acids of SEQ ID NO:2, where the
additional amino acid sequence is C-terminal to the at least 300
contiguous amino acids of SEQ ID NO:1. In some embodiments, the
polypeptide may additionally comprises a purification tag and/or an
exogenous sequence-specific DNA binding domain.
[0006] In some embodiments, the polypeptide may have reverse
transcriptase activity. In these embodiments, the polypeptide may
or may not have an RNAseH activity in addition to the reverse
transcriptase activity.
[0007] In general, a method for reverse transcribing an RNA
template is also provided. In some aspects, the method may
comprise: (a) combining a primer, an RNA template and a reverse
transcriptase comprising: i. at least 300 contiguous amino acids of
SEQ ID NO:1 and optionally ii. an amino acid sequence that is at
least 90% identical to at least 286 contiguous amino acids of SEQ
ID NO:2 that is C-terminal to the at least 300 contiguous amino
acids of SEQ ID NO:1, to produce a reaction mix and (b) incubating
the reaction mix to produce cDNA copied from the RNA template.
[0008] In some aspects, the reaction mix may comprise a template
switching oligonucleotide and in other aspects, the reaction mix
may incubated at temperature that is higher than 42.degree. C.,
e.g., at a temperature in the range of 45.degree. C. to 65.degree.
C. The primer in the reaction mix oligo-dT primer, a random primer
or a gene-specific primer, for example. As noted above, in some
cases, the polypeptide may comprise an exogenous sequence-specific
DNA binding domain and, may or may not have RNAseH activity.
[0009] In general, a method is provided for reverse transcribing an
RNA template wherein the population of cDNA molecules produced by
the method may be at least 20%, at least 40%, at least 60%, or at
least 80% full length. In other aspects, the method may comprise
transcribing, with increased efficiency compared with previously
available reverse transcriptases, GC rich template molecules using
embodiments of the reverse transcriptase described above where the
template molecules may have at least 20%, 30%, 40%, 50%, 60%, 70%
or 80% GC content. In embodiments, the cDNA product of the GC rich
template may be at least 20%, at least 40%, at least 60%, or at
least 80% full length.
[0010] These and other features of the present teachings are set
forth herein.
BRIEF DESCRIPTION OF THE FIGURES
[0011] The skilled artisan will understand that the drawings,
described below, are for illustration purposes only. The drawings
are not intended to limit the scope of the present teachings in any
way.
[0012] FIG. 1 shows some of the components used in the template
switching assay described in the Examples section.
[0013] FIG. 2 illustrates how reverse transcription efficiency can
be quantified.
[0014] FIG. 3 is a bar chart showing the relative reverse
transcription efficiencies of two commercially available MMLV
reverse transcriptase variants (SuperScript.RTM. IV (Life
Technologies, Carlsbad, Calif.) and ProtoScript.RTM. II (New
England Biolabs, Ipswich, Mass.) and the M19H variant in copying
RNA templates with differing GC content.
DETAILED DESCRIPTION OF EMBODIMENTS
[0015] Unless defined otherwise herein, all technical and
scientific terms used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. Although any methods and materials similar or
equivalent to those described herein can be used in the practice or
testing of the present invention, the preferred methods and
materials are described.
[0016] All patents and publications, including all sequences
disclosed within such patents and publications, referred to herein
are expressly incorporated by reference.
[0017] Numeric ranges are inclusive of the numbers defining the
range. Unless otherwise indicated, nucleic acids are written left
to right in 5' to 3' orientation; amino acid sequences are written
left to right in amino to carboxy orientation, respectively.
[0018] The headings provided herein are not limitations of the
various aspects or embodiments of the invention. Accordingly, the
terms defined immediately below are more fully defined by reference
to the specification as a whole.
[0019] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs.
Singleton, et al., DICTIONARY OF MICROBIOLOGY AND MOLECULAR
BIOLOGY, 2D ED., John Wiley and Sons, New York (1994), and Hale
& Markham, THE HARPER COLLINS DICTIONARY OF BIOLOGY, Harper
Perennial, N.Y. (1991) provide one of skill with the general
meaning of many of the terms used herein. Still, certain terms are
defined below for the sake of clarity and ease of reference.
[0020] As used herein, the term "reverse transcriptase" refers to
any DNA polymerase that can copy first-strand cDNA from an RNA
template. Such enzymes are commonly referred to as RNA-directed DNA
polymerases and have IUBMB activity EC 2.7.7.49. In some cases, a
reverse transcriptase can copy a complementary DNA strand using
either single-stranded RNA or DNA as a template. MMLV reverse
transcriptase is the reverse transcriptase of the Moloney murine
leukemia virus.
[0021] As used herein, the term "template" refers to the substrate
RNA for the reverse transcriptase to make cDNA. A template may be
complex (e.g., total RNA, polyA+ RNA, mRNA, etc.) or not complex
(e.g., an enriched RNA or an in vitro transcribed product).
[0022] The term "cDNA" refers to a strand of DNA copied from an RNA
template. cDNA is complementary to the RNA template.
[0023] A "mutant" or "variant" protein may have one or more amino
acid substitutions, deletions (including truncations) or additions
(including deletions) relative to a wild-type. A variant may have
less than 100% sequence identity to the amino acid sequence of a
naturally occurring protein but may have any amino acid that is at
least 80%, at least 85%, at least 90%, at least 95%, at least 97%,
at least 98% or at least 99% identical to the amino acid sequence
of the naturally occurring protein. A fusion protein is a type of
protein composed of a plurality of polypeptide components that are
unjoined in their naturally occurring state. Fusion proteins may be
a combination of two, three or even four or more different
proteins. The term polypeptide includes fusion proteins, including,
but not limited to, a fusion of two or more heterologous amino acid
sequences, a fusion of a polypeptide with: a heterologous targeting
sequence, a linker, an immunologically tag, a detectable fusion
partner, such as a fluorescent protein, .beta.-galactosidase,
luciferase, etc., and the like. A fusion protein may have one or
more heterologous domains added to the N-terminus, C-terminus, and
or the middle portion of the protein. If two parts of a fusion
protein are "heterologous", they are not part of the same protein
in its natural state.
[0024] The term "non-naturally occurring" refers to a composition
that does not exist in nature. Variant proteins are non-naturally
occurring. In some embodiments, "non-naturally occurring" refers to
a protein that has an amino acid sequence and/or a
post-translational modification pattern that is different to the
protein in its natural state. A non-naturally occurring protein may
have one or more amino acid substitutions, deletions or insertions
at the N-terminus, the C-terminus and/or between the N- and
C-termini of the protein. A "non-naturally occurring" protein may
have an amino acid sequence that is different to a naturally
occurring amino acid sequence (i.e., having less than 100% sequence
identity to the amino acid sequence of a naturally occurring
protein) but that that is at least 80%, at least 85%, at least 90%,
at least 95%, at least 97%, at least 98% or at least 99% identical
to the naturally occurring amino acid sequence. In certain cases, a
non-naturally occurring protein may contain an N-terminal
methionine or may lack one or more post-translational modifications
(e.g., glycosylation, phosphorylation, etc.) if it is produced by a
different (e.g., bacterial) cell.
[0025] In the context of a nucleic acid, the term "non-naturally
occurring" refers to a nucleic acid that contains: a) a sequence of
nucleotides that is different to a nucleic acid in its natural
state (i.e. having less than 100% sequence identity to a naturally
occurring nucleic acid sequence), b) one or more non-naturally
occurring nucleotide monomers (which may result in a non-natural
backbone or sugar that is not G, A, T or C) and/or c) may contain
one or more other modifications (e.g., an added label or other
moiety) to the 5'-end, the 3' end, and/or between the 5'- and
3'-ends of the nucleic acid.
[0026] In the context of a preparation, the term "non-naturally
occurring" refers to: a) a combination of components that are not
combined by nature, e.g., because they are at different locations,
in different cells or different cell compartments; b) a combination
of components that have relative concentrations that are not found
in nature; c) a combination that lacks something that is usually
associated with one of the components in nature; d) a combination
that is in a form that is not found in nature, e.g., dried, freeze
dried, crystalline, aqueous; and/or e) a combination that contains
a component that is not found in nature. For example, a preparation
may contain a "non-naturally occurring" buffering agent (e.g.,
Tris, HEPES, TAPS, MOPS, tricine or MES), a detergent, a dye, a
reaction enhancer or inhibitor, an oxidizing agent, a reducing
agent, a solvent or a preservative that is not found in nature.
[0027] The term "template-switching" refers to a reverse
transcription reaction in which the reverse transcriptase switches
template from an RNA molecule to a synthetic oligonucleotide (which
usually contains two or three Gs at its 3' end, thereby copying the
sequence of the synthetic oligonucleotide onto the end of the cDNA.
Template switching is generally described in Matz et al., Nucl.
Acids Res. 1999 27: 1558-1560 and Wu et al., Nat Methods. 2014 11:
41-6. In template switching (and as illustrated in FIG. 1) a primer
hybridizes to a RNA molecule. This primer serves as a primer for a
reverse transcriptase that copies the RNA molecule to form a
complementary cDNA molecule. In copying the RNA molecule, the
reverse transcriptase commonly travels beyond the 5' end of the
mRNA to add non-template nucleotides to the 3' end of the cDNA
(typically Cs). Addition of an oligonucleotide that has
ribonucleotides or deoxyribonucleotides that are complementary to
the non-template nucleotides added onto the cDNA (e.g., a "template
switching" oligonucleotide that typically has two or three Gs at
its 3' end), the reverse transcriptase will jump templates from the
RNA template to the oligonucleotide template, thereby producing a
cDNA molecule that has the complement of the template switching
oligonucleotide at it's 3' end.
[0028] The term "RNAseH activity" refers to an activity that
hydrolyzes the RNA in RNA/DNA hybrid. Many reverse transcriptases
have an RNAseH activity that can be inactivated by truncation or by
substitution.
[0029] The term "primer" refers to an oligonucleotide that is
capable, upon forming a duplex with a polynucleotide template, of
acting as a point of initiation of nucleic acid synthesis and being
extended from its 3' end along the template so that an extended
duplex is formed. The sequence of nucleotides added during the
extension process is determined by the sequence of the template
polynucleotide. Primers are of a length compatible with their use
in synthesis of primer extension products, and can are in the range
of between 8 to 100 nucleotides in length, such as 10 to 75, 15 to
60, 15 to 40, 18 to 30, 20 to 40, 21 to 50, 22 to 45, 25 to 40, and
so on, more typically in the range of between 18 to 40, 20 to 35,
21 to 30 nucleotides long, and any length between the stated
ranges. Primers are usually single-stranded. Primers have a 3'
hydroxyl.
[0030] The term "primer extension" as used herein refers to both to
the synthesis of DNA resulting from the polymerization of
individual nucleoside triphosphates using a primer as a point of
initiation, and to the joining of additional oligonucleotides to
the primer to extend the primer. Primers can incorporate additional
features which allow for the detection or immobilization of the
primer but do not alter the basic property of the primer, that of
acting as a point of initiation of DNA synthesis. For example,
primers may contain an additional nucleic acid sequence at the 5'
end which does not hybridize to the target nucleic acid, but which
facilitates cloning of the amplified product. The region of the
primer which is sufficiently complementary to the template to
hybridize is referred to herein as the hybridizing region. The
terms "target region" and "target nucleic acid" refers to a region
or subsequence of a nucleic acid which is to be reverse
transcribed.
[0031] A polypeptide comprising at least 300 contiguous amino acids
of SEQ ID NO:1 is provided. The first 23 amino acids can be removed
from MMLV reverse transcriptase without altering the polymerase
activity of that enzyme (see, e.g., Gu et al., J. Mol. Biol. 305:
341-359, Najmudin et al, J. Mol. Biol. 296 613-632 and Das et al.,
Protein Sci. 2001 10: 1936-1941). As such, some embodiments, the
polypeptide may have a truncated N-terminus relative to SEQ ID
NO:1. In some embodiments, the polypeptide may comprises amino acid
residues 24-335 of SEQ ID NO:1, e.g., the entire contiguous
sequence of SEQ ID NO:1. The present polypeptide may contain 5, 6,
or 7 or more amino acid substitutions relative to the corresponding
sequence in the wild type MMLV reverse transcriptase.
[0032] The polypeptide may additionally comprise an amino acid
sequence that is at least 90% (e.g., at least 95%, at least 98%, at
least 99% or at least 100%) identical to at least 286 contiguous
amino acids (e.g., at least 300 contiguous amino acids, at least
325 contiguous amino acids or at least 336 contiguous amino acids)
of SEQ ID NO:2, where SEQ ID NO:2 is the sequence of the C-terminal
part of an MMLV reverse transcriptase, shown below:
TABLE-US-00001 (SEQ ID NO: 2)
WGPDQQKAYQEIKQALLTAPALGLPDLTKPFELFVDEKQGYAKGVLTQKL
GPWRRPVAYLSKKLDPVAAGWPPCLRMVAAIAVLTKDAGKLTMGQPLVIL
APHAVEALVKQPPDRWLSNARMTHYQALLLDTDRVQFGPVVALNPATLLP
LPEEGLQHNCLDILAEAHGTRPDLTDQPLPDADHTWYTDGSSLLQEGQRK
AGAAVTTETEVIWAKALPAGTSAQRAELIALTQALKMAEGKKLNVYTDSR
YAFATAHIHGEIYRRRGLLTSEGKEIKNKDEILALLKALFLPKRLSIIHC
PGHQKGHSAEARGNRMADQAARKAAITETPDTSTLLIENSSPNSRLIN
[0033] This additional sequence may be positioned C-terminal to the
at least 300 contiguous amino acids of SEQ ID NO: 1. It is known
that as many as 62 residues can be removed from the C-terminus of
the MMLV reverse transcriptase (see, e.g., U.S. Pat. No. 5,017,492)
without significantly altering the polymerase activity. As such, in
some embodiments, the additional amino acid sequence may lack the
C-terminal 3, 5, 10, 12, 15, 30, 50 or 62 amino acids of SEQ ID
NO:2.
[0034] The MMLV reverse transcriptase has been crystallized (see,
e.g., Das et al., Structure. 2004 12: 819-29), the
structure-functional relationships in MMLV reverse transcriptase
have been studied (see, e.g., Cote et al., Virus Res. 2008 134:
186-202, Georgiadis et al., Structure. 1995 3: 879-92 and Crowther
et al., Proteins 2004 57: 15-26) and many mutations in MMLV reverse
transcriptase are known (see, e.g., Yasukawa et al., J. Biotechnol.
2010 150: 299-306, Arezi et al Nucleic Acids Res. 2009 37: 473-81
and Konishi et al., Biochem. Biophys. Res. Commun. 2014 454:269-74,
among many others). It is also known that one can truncate the MMLV
reverse transcriptase from either ends, and add exogenous sequences
to either end (see, e.g., U.S. Pat. No. 5,017,492), without
abolishing activity. As such, MMLV reverse transcriptase variants
are well known.
[0035] In some embodiments, the polypeptide may additionally
comprises an exogenous domain and/or a purification tag (e.g., a
His tag or the like) at either terminus. In some embodiments, the
polypeptide may comprise a sequence-specific DNA binding protein
domain, which domain has been shown to increase the processivity of
other polymerases (see, e.g., US 2016/0160193). In some embodiments
the sequence-specific DNA binding protein domain may be a DNA
binding protein domain listed in the following table (as found in
US 2016/0160193).
TABLE-US-00002 DNA-binding protein Tfx BD-51 gi|499321160
AbrB/MazE/MraZ-like BD-52 gi|499321199 "Winged helix" DNA-binding
domain BD-54 gi|499322061 Ribbon-helix-helix protein, copG family
BD-62 gi|499321149 lambda repressor-like DNA-binding domains BD-63
gi|499322443 Resolvase-like BD-67 gi|499322676 "Winged helix"
DNA-binding domain BD-71 gi|499322676 "Winged helix" DNA-binding
domain BD-74 gi|499322255 "Winged helix" DNA-binding domain BD-75
gi|499322388 "Winged helix" DNA-binding domain BD-81 gi|499322131
"Winged helix" DNA-binding domain BD-82 gi|499321342 "Winged helix"
DNA-binding domain BD-85 gi|499321130 "Winged helix" DNA-binding
domain BD-86 gi|499322705 "Winged helix" DNA-binding domain BD-88
gi|499320855 "Winged helix" DNA-binding domain BD-89 gi|499322250
"Winged helix" DNA-binding domain BD-91 gi|499321633 "Winged helix"
DNA-binding domain BD-92 gi|490170077 "Winged helix" DNA-binding
domain BD-93 gi|499321272 "Winged helix" DNA-binding domain BD-94
gi|499320919 "Winged helix" DNA-binding domain BD-97 gi|499320853
"Winged helix" DNA-binding domain BD-98 gi|499321734 "Winged helix"
DNA-binding domain BD-100 gi|499322439 "Winged helix" DNA-binding
domain BD-102 gi|499322707 "Winged helix" DNA-binding domain BD-109
gi|499321112 HCP-like BD-02 gi|351675391 Helix-turn-helix domain,
rpiR family BD-03 gi|500479591 Helix-turn-helix domain, rpiR family
BD-04 gi|15643984 Bacterial regulatory proteins, lacl family BD-07
gi|15643711 Bacterial regulatory proteins, lacl family BD-08
gi|15643974 Bacterial regulatory proteins, lacl family BD-09
gi|15643956 Bacterial regulatory proteins, lacl family BD-11
gi|500480095 lambda repressor-like DNA-binding domains BD-12
gi|15643421 "Winged helix" DNA-binding domain BD-14 gi|15644350
"Winged helix" DNA-binding domain BD-16 gi|24159093 "Winged helix"
DNA-binding domain BD-18 gi|15643139 "Winged helix" DNA-binding
domain BD-23 gi|15642807 "Winged helix" DNA-binding domain BD-24
gi|15643159 "Winged helix" DNA-binding domain BD-30 gi|15643333
"Winged helix" DNA-binding domain BD-32 gi|15643055 "Winged helix"
DNA-binding domain BD-37 gi|15643827 "Winged helix" DNA-binding
domain BD-43 gi|15643699 Homeodomain-like BD-45 gi|15643788
[0036] In some embodiments, the polypeptide may have reverse
transcriptase activity. In these embodiments, the polypeptide may
or may not have an RNAseH activity in addition to the reverse
transcriptase activity. Examples of MMLV reverse transcriptase that
lack the RNAseH activity are known (see, e.g., Kotewicz et al.,
Nucleic Acids Res. 1988 16: 265-77 and Schultz et al., J. Virol.
1996 70: 8630-8).
[0037] A method for reverse transcribing an RNA template is also
provided. In some embodiments, this method may comprise: (a)
combining a primer, an RNA template, a reverse transcriptase
comprising: i. at least 300 contiguous amino acids of SEQ ID NO:1,
as described above, and ii. an amino acid sequence that is at least
90% identical to at least 286 contiguous amino acids of SEQ ID NO:2
(as described above) that is C-terminal to the at least 300
contiguous amino acids of SEQ ID NO:1, as well as any other
components that may be necessary or desirable to perform a reverse
transcription (e.g., salt, nucleotides, RNAse inhibitor, buffer,
etc.), to produce a reaction mix; and (b) incubating the reaction
mix to produce cDNA copied from the RNA template. The RNA template
may be any type of RNA template, e.g., total RNA, polyA.sup.+ RNA,
capped RNA, enriched RNA etc., and the RNA can be from any source,
e.g., bacteria, mammals, an in vitro transcription reaction, etc.,
methods for the making of which are known. The RNA template may
contain RNA molecules that are at least 1 kb in length, e.g., at
least 2 kb, at least 3 kb or at least 5 kb and, in some
embodiments, at least some of the molecules in the RNA template may
have a GC content of at least 50%, at least 60%, at least 70%, or
at least 80%. The primer in the reaction mix may be any type of
primer, e.g., an oligo-dT primer, a random primer or a
gene-specific primer, for example, which primers are commonly used
to make cDNA. In some embodiments, the reaction mix may comprise a
template switching oligonucleotide, as described above.
[0038] In some embodiments, the reaction mix may be incubated at
temperature that is higher than 42.degree. C., e.g., at a
temperature in the range of 45.degree. C. to 60.degree. C. In some
embodiments, the reaction mix may be incubated at a temperature in
the range of 42.degree. C. to 45.degree. C., 48.degree. C. to
51.degree. C., 51.degree. C. to 54.degree. C., 54.degree. C. to
57.degree. C., 57.degree. C. to 60.degree. C. or 60.degree. C. to
65.degree. C. In some embodiments, the population of cDNA molecules
produced by the method may be at least 20%, at least 40%, at least
60%, or at least 80% full length. The polymerase can reverse
transcribe GC rich template molecules with increased efficiency
compared with previously available reverse transcriptases where the
template molecules may have at least 20%, 30%, 40%, 50%, 60%, 70%
or 80% GC content (see for example, FIG. 3).
[0039] If an oligo-dT or a random primer is used in the method,
then the may be used to make a cDNA library that can be sequenced
or used for gene expression analysis. Alternatively, if a
gene-specific primer is used, then method may be used for RT-PCR
(e.g., quantitative RT-PCR) and other similar analyses.
[0040] All references cited herein are incorporated by
reference.
Examples
[0041] Aspects of the present teachings can be further understood
in light of the following examples, which should not be construed
as limiting the scope of the present teachings in any way.
[0042] Superscript IV, Protoscript II and a variant MMLV reverse
transcriptase referred to as "M19H" were tested in a template
switching assay to determine the efficiency of reverse
transcription of templates that have different GC contents (14% to
88.6%). The M19H mutant comprises the following N-terminal
sequence:
TABLE-US-00003 (SEQ ID NO: 1)
TLNIEDEYRLHETSKEPDVSLGSTWLSDFPQAWAETGGMGLAVRQAPLII
PLKATATPVSIKQYPMSQEARLGIKPHIQRLLDQGILVPCQSPWNTPLLP
VKKPGTNDYRPVQDLREVNKRVEDIHPTVPNPYNLLSGLPPSHQWYTVLD
LKDAFFCLRLHPTSQPLFAFEWRDPEMGISGQLTWTRLPQGFKNSPTLFD
EALHRDLADFRIQHPDLILLQYVDDLLLAATSELDCQQGTRALLQELGDL
GYRASAKKAQICQKQVKYLGYLLKEGQRWLTEARKETVMGIPTPKTPRQL
REFLGTAGFCRLWIPGFAELAAPLYPLTKEGTLFN
[0043] A template switching assay was performed. 0.5 .mu.l of 2
.mu.M RNA transcript (200 to 330 nucleotides in length) of varying
GC content (from 14% to 88.6%), 0.3 .mu.l of 1 .mu.M FAM primer, 1
.mu.l of 10 mM dNTP, 0.25 .mu.l of RNase Inhibitor, 1 .mu.l of 10
.mu.M template switching oligonucleotide (oligo) and 0.5 .mu.l of
reverse transcriptase were combined in a 10 .mu.l reaction volume
(using a buffer: 50 mM Tris-HCl, 75 mM KCl, 3 mM MgCl.sub.2, pH
8.3). The reaction was incubated at a designated temperature (e.g.,
50.degree. C.) for 90 minutes followed by inactivation step at
72.degree. C. for 10 minutes. After the reaction, incomplete
products, full length products, and template switched products were
quantified by a capillary electrophoresis assay (see Beckman
Coulter (Indianapolis, Ind.) "Introduction to Capillary
Electrophoresis"). The areas under the peak of incompletion,
elongation and template switching products were measured. The
transcription efficiency equals to the sum of elongation and
template switching divided by the sum of incompletion, elongation
and template switching. The relationships between the components
used in the assay are shown in FIG. 1. An example of how a
capillary electrophoresis chromatogram can be to quantify the
incomplete products, full length products, and template switched
products is shown in FIG. 2.
[0044] Based on the results shown in FIG. 3, the M19H enzyme
appears to be more efficient than Superscript IV and Protoscript
II, particularly for more GC-rich templates, under the conditions
used.
Sequence CWU 1
1
21335PRTArtificial SequenceSynthetic construct 1Thr Leu Asn Ile Glu
Asp Glu Tyr Arg Leu His Glu Thr Ser Lys Glu 1 5 10 15 Pro Asp Val
Ser Leu Gly Ser Thr Trp Leu Ser Asp Phe Pro Gln Ala 20 25 30 Trp
Ala Glu Thr Gly Gly Met Gly Leu Ala Val Arg Gln Ala Pro Leu 35 40
45 Ile Ile Pro Leu Lys Ala Thr Ala Thr Pro Val Ser Ile Lys Gln Tyr
50 55 60 Pro Met Ser Gln Glu Ala Arg Leu Gly Ile Lys Pro His Ile
Gln Arg 65 70 75 80 Leu Leu Asp Gln Gly Ile Leu Val Pro Cys Gln Ser
Pro Trp Asn Thr 85 90 95 Pro Leu Leu Pro Val Lys Lys Pro Gly Thr
Asn Asp Tyr Arg Pro Val 100 105 110 Gln Asp Leu Arg Glu Val Asn Lys
Arg Val Glu Asp Ile His Pro Thr 115 120 125 Val Pro Asn Pro Tyr Asn
Leu Leu Ser Gly Leu Pro Pro Ser His Gln 130 135 140 Trp Tyr Thr Val
Leu Asp Leu Lys Asp Ala Phe Phe Cys Leu Arg Leu 145 150 155 160 His
Pro Thr Ser Gln Pro Leu Phe Ala Phe Glu Trp Arg Asp Pro Glu 165 170
175 Met Gly Ile Ser Gly Gln Leu Thr Trp Thr Arg Leu Pro Gln Gly Phe
180 185 190 Lys Asn Ser Pro Thr Leu Phe Asp Glu Ala Leu His Arg Asp
Leu Ala 195 200 205 Asp Phe Arg Ile Gln His Pro Asp Leu Ile Leu Leu
Gln Tyr Val Asp 210 215 220 Asp Leu Leu Leu Ala Ala Thr Ser Glu Leu
Asp Cys Gln Gln Gly Thr 225 230 235 240 Arg Ala Leu Leu Gln Glu Leu
Gly Asp Leu Gly Tyr Arg Ala Ser Ala 245 250 255 Lys Lys Ala Gln Ile
Cys Gln Lys Gln Val Lys Tyr Leu Gly Tyr Leu 260 265 270 Leu Lys Glu
Gly Gln Arg Trp Leu Thr Glu Ala Arg Lys Glu Thr Val 275 280 285 Met
Gly Ile Pro Thr Pro Lys Thr Pro Arg Gln Leu Arg Glu Phe Leu 290 295
300 Gly Thr Ala Gly Phe Cys Arg Leu Trp Ile Pro Gly Phe Ala Glu Leu
305 310 315 320 Ala Ala Pro Leu Tyr Pro Leu Thr Lys Glu Gly Thr Leu
Phe Asn 325 330 335 2348PRTArtificial SequenceSynthetic construct
2Trp Gly Pro Asp Gln Gln Lys Ala Tyr Gln Glu Ile Lys Gln Ala Leu 1
5 10 15 Leu Thr Ala Pro Ala Leu Gly Leu Pro Asp Leu Thr Lys Pro Phe
Glu 20 25 30 Leu Phe Val Asp Glu Lys Gln Gly Tyr Ala Lys Gly Val
Leu Thr Gln 35 40 45 Lys Leu Gly Pro Trp Arg Arg Pro Val Ala Tyr
Leu Ser Lys Lys Leu 50 55 60 Asp Pro Val Ala Ala Gly Trp Pro Pro
Cys Leu Arg Met Val Ala Ala 65 70 75 80 Ile Ala Val Leu Thr Lys Asp
Ala Gly Lys Leu Thr Met Gly Gln Pro 85 90 95 Leu Val Ile Leu Ala
Pro His Ala Val Glu Ala Leu Val Lys Gln Pro 100 105 110 Pro Asp Arg
Trp Leu Ser Asn Ala Arg Met Thr His Tyr Gln Ala Leu 115 120 125 Leu
Leu Asp Thr Asp Arg Val Gln Phe Gly Pro Val Val Ala Leu Asn 130 135
140 Pro Ala Thr Leu Leu Pro Leu Pro Glu Glu Gly Leu Gln His Asn Cys
145 150 155 160 Leu Asp Ile Leu Ala Glu Ala His Gly Thr Arg Pro Asp
Leu Thr Asp 165 170 175 Gln Pro Leu Pro Asp Ala Asp His Thr Trp Tyr
Thr Asp Gly Ser Ser 180 185 190 Leu Leu Gln Glu Gly Gln Arg Lys Ala
Gly Ala Ala Val Thr Thr Glu 195 200 205 Thr Glu Val Ile Trp Ala Lys
Ala Leu Pro Ala Gly Thr Ser Ala Gln 210 215 220 Arg Ala Glu Leu Ile
Ala Leu Thr Gln Ala Leu Lys Met Ala Glu Gly 225 230 235 240 Lys Lys
Leu Asn Val Tyr Thr Asp Ser Arg Tyr Ala Phe Ala Thr Ala 245 250 255
His Ile His Gly Glu Ile Tyr Arg Arg Arg Gly Leu Leu Thr Ser Glu 260
265 270 Gly Lys Glu Ile Lys Asn Lys Asp Glu Ile Leu Ala Leu Leu Lys
Ala 275 280 285 Leu Phe Leu Pro Lys Arg Leu Ser Ile Ile His Cys Pro
Gly His Gln 290 295 300 Lys Gly His Ser Ala Glu Ala Arg Gly Asn Arg
Met Ala Asp Gln Ala 305 310 315 320 Ala Arg Lys Ala Ala Ile Thr Glu
Thr Pro Asp Thr Ser Thr Leu Leu 325 330 335 Ile Glu Asn Ser Ser Pro
Asn Ser Arg Leu Ile Asn 340 345
* * * * *