CN114480335A

CN114480335A - Reverse transcriptase and reverse transcription detection reagent

Info

Publication number: CN114480335A
Application number: CN202011271781.XA
Authority: CN
Inventors: 蒋析文; 刘霭珊; 连献兰; 谢晓成
Original assignee: Guangzhou Da'an Gene Co ltd
Current assignee: Guangzhou Da'an Gene Co ltd
Priority date: 2020-11-13
Filing date: 2020-11-13
Publication date: 2022-05-13

Abstract

The invention provides a reverse transcriptase and a reverse transcription detection reagent, and particularly relates to a reverse transcriptase (M-MLV) mutant library, a reverse transcriptase mutant with high thermal stability and high amplification efficiency is finally screened out through a large amount of screening, and the reverse transcription detection reagent containing the reverse transcriptase mutant is further provided.

Description

Reverse transcriptase and reverse transcription detection reagent

Technical Field

The invention belongs to the technical field of biology, and particularly relates to a reverse transcriptase for nucleic acid detection and a reverse transcription detection reagent.

Background

Murine leukemia reverse transcriptase (M-MLV) is a DNA polymerase using RNA as a template, has RNase H activity and no 3 '-5' exonuclease activity, and can be used for reverse transcription to synthesize cDNA. RNA has a more complex secondary structure, and therefore has a greater influence on the reverse transcription efficiency of the M-MLV enzyme. The simplest method for opening the secondary structure of RNA is to open the hydrogen bonds of the secondary structure by high temperature and the RNA becomes linear single-stranded. However, the wild-type M-MLV enzyme had an optimum reaction temperature of 37 ℃ and decreased stability and activity at high temperatures. Therefore, the improvement of the thermal stability of the M-MLV enzyme through mutation and the adaptation to the reaction at high temperature are the main modification directions of the M-MLV enzyme.

The M-MLV enzyme is subjected to mutation modification by the following routes:

1. and (4) randomly mutating. Random mutation is carried out on the M-MLV full-length sequence or a certain structural domain, and then screening is carried out. The method can screen MMLV mutants with high activity and high thermal stability, but the technical process is complicated, and the library capacity of the mutation generated by random mutation can reach 10⁷With a large number of inactive mutations, the screening difficulty is great. (reference: Arezi B, Hogrefe H. novel statistics in Moloney Murine Leukemia Virus reverse transcription in giant robustness Lighting combining to template-primer [ J].Nucleic Acids Research,2008,37(2):473-481.)

2. Site-directed mutagenesis is performed on a specific active site. The method has strong pertinence, and improves the enzyme activity by increasing the affinity of amino acid of key active sites such as nucleic acid binding sites, metal ion binding sites and the like with a substrate. However, this method lacks analysis of the overall structure of the enzyme and cannot improve the stability of the enzyme as a whole. (reference: Yasukawa K, Mizuno M, Konishi A, et al, incorporated in thermal stability of Moloney Murine leukamia virus reverse transcriptase by site-directed mutagenesis [ J ] Journal of Biotechnology,2010,150(3): 299. 306.)

In general, due to the complexity of the protein structure, not only the amino acids located at the active site, but also some amino acids far away from the active site, may have an influence on the overall structure and performance of the enzyme, so there is great uncertainty in the modification of the enzyme.

Disclosure of Invention

The present invention aims to provide a reverse transcriptase mutant which is resistant to high temperature and has high reverse transcription efficiency.

In a first aspect of the present invention, there is provided an M-MLV enzyme mutant which is mutated at least two (which may be two, three, four, or five) sites selected from the group consisting of: 446 th amino acid residue, 313 rd amino acid residue, 583 rd amino acid residue, 607 th amino acid residue and 221 th amino acid residue, wherein the numbering of the amino acid residues adopts the numbering shown in SEQ ID NO. 1.

The amino acid sequence of the corresponding wild type murine leukemia reverse transcriptase (M-MLV) is shown in SEQ ID NO. 1.

In another preferred example, in the M-MLV enzyme mutant, the 446 th amino acid residue position is mutated to Cys.

In another preferred example, in the M-MLV enzyme mutant, the 313 th amino acid residue position is mutated into His or Gln.

In another preferred embodiment, in the M-MLV enzyme mutant, the position of the 583 th amino acid residue is mutated into Asn.

In another preferred embodiment, in the M-MLV enzyme mutant, the 607 th amino acid residue position is mutated to Lys.

In another preferred embodiment, in the M-MLV enzyme mutant, the 221 th amino acid residue position is mutated to Arg.

In another preferred embodiment, the amino acid sequence of said M-MLV enzyme mutant has at least about 80% homology to SEQ ID No. 1; more preferably, at least about 90% homology; most preferably, at least about 95% homology; such as at least about 96%, 97%, 98%, 99% homology.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 583, and amino acid residue 313.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 313 and amino acid residue 221.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 583, and amino acid residue 446.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 583, and amino acid residue 221.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 313 and amino acid residue 446.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 313 and amino acid residue 607.

In another preferred embodiment, the M-MLV enzyme mutant has a mutation at amino acid residue 313, amino acid residue 583, and amino acid residue 221.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 313, amino acid residue 583, and amino acid residue 607.

In another preferred embodiment, the M-MLV enzyme mutant has a mutation at amino acid residue 313, amino acid residue 583, and amino acid residue 446.

In another preferred example, the M-MLV enzyme mutant has a 10-fold or more, preferably 20-fold or more, more preferably 30-fold or more, increase in reverse transcription efficiency at high temperature (58 ℃) compared to the wild type.

In a second aspect of the invention, there is provided a polynucleotide molecule encoding an M-MLV enzyme mutant according to the first aspect of the invention.

In a third aspect of the invention, there is provided a vector comprising a nucleic acid molecule according to the second aspect of the invention.

In a fourth aspect of the invention, there is provided a host cell comprising a vector according to the first aspect of the invention or a chromosome into which a nucleic acid molecule according to the second aspect of the invention has been integrated.

In another preferred embodiment, the host cell is a prokaryotic cell, or a eukaryotic cell.

In another preferred embodiment, the prokaryotic cell is E.coli.

In another preferred embodiment, the eukaryotic cell is a yeast cell.

In a fifth aspect of the present invention, there is provided a method for preparing the M-MLV enzyme mutant according to the first aspect of the present invention, comprising the steps of:

(i) culturing the host cell of the fourth aspect of the invention under suitable conditions to express the M-MLV enzyme mutant; and

(ii) isolating said M-MLV enzyme mutant.

In another preferred example, the temperature at which the host cell is cultured in step (i) is 20 ℃ to 40 ℃; preferably from 25 ℃ to 37 ℃, e.g. 35 ℃.

In a sixth aspect of the invention, there is provided a kit comprising the M-MLV enzyme mutant of the first aspect of the invention.

In another preferred embodiment, the kit further comprises one or more components selected from the group consisting of:

dNTP, buffer, primer, probe, and pure water.

In a seventh aspect of the invention, there is provided a use of the M-MLV enzyme mutant of the first aspect of the invention in the preparation of a reverse transcription detection reagent or a reverse transcription kit.

In an eighth aspect of the present invention, there is provided a method for reverse transcription of RNA, the method comprising the steps of:

(1) providing a sample containing RNA;

(2) reverse transcription reaction

Performing a reverse transcription reaction on the RNA-containing sample provided in step (1) using the reverse transcriptase mutant according to the first aspect of the present invention.

In another preferred example, in the step (2), the reverse transcription reaction temperature is 55 ℃ or more, preferably 58 ℃ or more.

It is to be understood that within the scope of the present invention, the above-described features of the present invention and those specifically described below (e.g., in the examples) may be combined with each other to form new or preferred embodiments. Not to be reiterated herein, but to the extent of space.

Detailed Description

The present inventors have made extensive and intensive studies to construct a reverse transcriptase (M-MLV) mutant library, and finally screened mutants having improved thermostability and higher amplification efficiency by stepwise screening. On the basis of this, the present invention has been completed.

Before the present invention is described, it is to be understood that this invention is not limited to the particular methodology and experimental conditions described, as such methodologies and conditions may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

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. As used herein, the term "about" when used in reference to a specifically recited value means that the value may vary by no more than 1% from the recited value. For example, as used herein, the expression "about 100" includes 99 and 101 and all values in between (e.g., 99.1, 99.2, 99.3, 99.4, etc.).

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 now exemplified.

Reverse transcriptase

Reverse transcriptase (reverse transcriptase) is also known as RNA-dependent DNA polymerase. The enzyme uses RNA as a template, dNTP as a substrate, tRNA (mainly tryptophan tRNA) as a primer, and synthesizes a DNA single strand which is complementary with the RNA template according to the base pairing principle on the 3' -OH end of tRNA and the 5' -3' direction, wherein the DNA single strand is called complementary DNA (cDNA).

Reverse transcriptase can be used for first strand cDNA synthesis, cDNA probe preparation, RNA transcription, sequencing, and reverse transcription of RNA. Commonly used reverse transcriptases in the art include murine leukemia virus (M-MLV) reverse transcriptase and Avian Myeloblastosis Virus (AMV) reverse transcriptase.

In a preferred embodiment of the invention, the wild-type M-MLV protein sequence of the invention is as follows:

TLNIEDEHRLHETSKEPDVSLGSTWLSDFPQAWAETGGMGLAVRQAPLIIPLKATSTPVSIKQYPMSQEARLGIKPHIQRLLDQGILVPCQSPWNTPLLPVKKPGTNDYRPVQDLREVNKRVEDIHPTVPNPYNLLSGLPPSHQWYTVLDLKDAFFCLRLHPTSQPLFAFEWRDPEMGISGQLTWTRLPQGFKNSPTLFDEALHRDLADFRIQHPDLILLQYVDDLLLAATSELDCQQGTRALLQTLGNLGYRASAKKAQICQKQVKYLGYLLKEGQRWLTEARKETVMGQPTPKTPRQLREFLGTAGFCRLWIPGFAEMAAPLYPLTKTGTLFNWGPDQQKAYQEIKQALLTAPALGLPDLTKPFELFVDEKQGYAKGVLTQKLGPWRRPVAYLSKKLDPVAAGWPPCLRMVAAIAVLTKDAGKLTMGQPLVILAPHAVEALVKQPPDRWLSNARMTHYQALLLDTDRVQFGPVVALNPATLLPLPEEGLQHNCLDILAEAHGTRPDLTDQPLPDADHTWYTDGSSLLQEGQRKAGAAVTTETEVIWAKALPAGTSAQRAELIALTQALKMAEGKKLNVYTDSRYAFATAHIHGEIYRRRGLLTSEGKEIKNKDEILALLKALFLPKRLSIIHCPGHQKGHSAEARGNRMADQAARKAAITETPDTSTLL(SEQ ID NO.:1)

in a preferred embodiment of the invention, the codon-optimized wild-type M-MLV DNA sequence (WT) is as follows:

ACGCTGAATATCGAGGACGAACACCGTCTGCACGAAACCAGCAAGGAGCCGGACGTTAGTCTGGGTAGCACGTGGCTGAGCGATTTTCCACAAGCGTGGGCGGAAACCGGTGGTATGGGTCTCGCCGTTCGCCAAGCCCCACTCATTATCCCACTGAAAGCCACGAGCACGCCGGTGAGCATCAAGCAGTACCCGATGAGCCAAGAAGCCCGCCTCGGCATTAAACCGCATATTCAGCGTCTGCTGGACCAAGGCATTCTGGTGCCGTGCCAGAGTCCGTGGAATACGCCACTGCTCCCGGTTAAGAAGCCGGGCACCAACGATTATCGCCCGGTTCAAGACCTCCGCGAAGTGAACAAGCGCGTGGAAGATATCCATCCGACCGTGCCAAATCCGTACAATCTGCTGAGTGGCCTCCCGCCGAGTCATCAATGGTACACCGTGCTGGATCTCAAGGATGCGTTTTTCTGCCTCCGTCTGCATCCAACCAGCCAGCCACTCTTTGCGTTTGAGTGGCGCGACCCAGAAATGGGTATCAGCGGTCAACTGACGTGGACGCGTCTGCCGCAAGGCTTCAAAAACAGCCCGACGCTGTTCGATGAGGCCCTCCATCGCGATCTGGCGGATTTCCGTATCCAGCATCCAGATCTGATTCTGCTGCAGTACGTTGACGATCTGCTCCTCGCGGCCACCAGTGAACTGGATTGCCAGCAAGGTACCCGTGCGCTGCTGCAGACGCTGGGCAATCTGGGCTACCGTGCCAGCGCGAAAAAGGCGCAAATCTGCCAGAAGCAAGTTAAGTACCTCGGTTATCTGCTGAAAGAGGGTCAACGCTGGCTGACCGAGGCGCGTAAAGAGACCGTTATGGGTCAGCCAACGCCAAAGACGCCACGCCAGCTCCGCGAATTTCTGGGTACCGCCGGCTTCTGTCGTCTGTGGATTCCGGGCTTCGCGGAAATGGCGGCGCCACTCTACCCGCTGACCAAAACCGGTACCCTCTTCAATTGGGGCCCAGATCAGCAGAAGGCCTACCAAGAAATTAAACAAGCGCTGCTCACCGCGCCGGCC CTCGGTCTCCCAGATCTGACCAAACCGTTTGAGCTGTTCGTGGACGAGAAGCAAGGCTACGCCAAAGGCGTGCTGACCCAGAAACTCGGTCCATGGCGTCGTCCGGTGGCCTACCTCAGTAAGAAACTGGATCCAGTTGCGGCGGGTTGGCCGCCATGTCTCCGTATGGTGGCGGCGATTGCCGTTCTGACCAAAGACGCCGGCAAACTCACCATGGGTCAGCCGCTGGTTATTCTCGCCCCACATGCGGTGGAAGCGCTGGTTAAACAACCGCCAGACCGCTGGCTGAGCAATGCCCGCATGACCCATTATCAAGCGCTGCTGCTGGACACCGACCGCGTTCAGTTCGGTCCGGTGGTTGCGCTGAATCCAGCGACGCTGCTGCCGCTGCCAGAAGAAGGTCTGCAGCACAACTGTCTGGACATTCTGGCCGAGGCCCATGGCACCCGTCCAGATCTCACCGATCAGCCACTGCCAGACGCCGATCATACGTGGTACACCGATGGTAGTAGTCTGCTGCAAGAAGGTCAACGTAAAGCGGGTGCCGCGGTGACGACGGAAACCGAGGTGATCTGGGCCAAAGCGCTGCCAGCGGGTACCAGCGCGCAACGTGCGGAACTGATCGCGCTGACCCAAGCGCTCAAAATGGCCGAGGGCAAGAAACTCAACGTGTACACCGACAGTCGCTACGCGTTTGCGACCGCGCACATCCACGGTGAGATTTATCGCCGCCGTGGTCTGCTCACGAGCGAAGGTAAGGAGATCAAGAATAAGGACGAGATCCTCGCGCTGCTGAAAGCCCTCTTTCTGCCGAAACGTCTGAGCATCATCCATTGCCCGGGTCACCAGAAGGGCCACAGTGCGGAAGCGCGCGGTAATCGCATGGCCGATCAAGCCGCGCGCAAAGCGGCGATTACGGAAACCCCGGATACGAGCACGCTGCTG(SEQ ID NO.:2)

screening and preparation of mutants

The invention calculates the change value (DDG) of Gibbs free energy change of the enzyme molecule after single point mutation so as to measure the change of the stability of the mutated molecule. The DDG value (Delta Delta Delta G) is the change value of Gibbs free energy change of the molecule, the energy consumption is required in the process of the protein molecule from a normal folding state to a random rolling state, the energy value is a Delta G value, the Delta G value can be used for measuring the stability of the protein, the higher the Delta G value is, the more energy is consumed in the protein denaturation, the higher the temperature for causing the protein denaturation is, and the more stable the protein is.

The protein is subjected to site-directed mutagenesis, the interaction of all amino acids is changed, the delta G value is changed, and the difference value of the delta G value of the wild-type protein and the delta G value of the mutant is the DDG value. DDG value >0, indicating that the Δ G value of the mutated protein is lower than that of the wild type, and the protein is more unstable; DDG value is less than 0, which indicates that the delta G value of the protein is increased after mutation and the protein is more stable than the wild type. Therefore, the DDG value can be used for predicting the structural stability change of the protein after site-directed mutagenesis. Selecting mutation with higher DDG value from a series of mutants, constructing an MMLV protein mutation library, performing expression and purification, determining the activity and the thermal stability of the MMLV after mutation, and screening out single-point mutants with high activity and high thermal stability. However, due to the complexity of the protein structure, it is impossible to obtain mutants meeting the requirements of practical application only by prediction, and in most cases the mutants predicted by simulation result in a significant reduction in enzyme activity.

Through a large amount of screening, 6 mutant sites which can lead the M-MLV enzyme to obtain high temperature resistance and high activity are screened out as follows:

the 6 mutation sites are combined to construct 10 MMLV mutants, and the MMLV mutants with better performance than the 6 single-point mutations are obtained.

Thus, in a preferred embodiment of the present invention, the present invention provides an M-MLV enzyme mutant which is mutated at least two (which may be two, three, four, or five) sites selected from the group consisting of: 446 th amino acid residue, 313 rd amino acid residue, 583 rd amino acid residue, 607 th amino acid residue and 221 th amino acid residue, wherein the numbering of the amino acid residues adopts the numbering shown in SEQ ID NO. 1.

In a preferred embodiment, the M-MLV enzyme mutants of the invention are as follows:

the M-MLV enzyme mutant has a 10-fold or more improved reverse transcription efficiency at high temperature (58 ℃) compared to the wild type, preferably 20-fold or more, more preferably 30-fold or more.

In a preferred embodiment, the reverse transcription efficiency test method is as follows:

extracting total RNA from Hela cell as template, and performing reverse transcription reaction according to the following system

Reacting the wild type and the mutant MMLV protein according to the system, and inactivating at 58 ℃ for 15 minutes and 75 ℃ for 5 minutes; then taking the reverse transcription product, and carrying out fluorescent quantitative PCR detection according to the following system

Q-PCR procedure: 95 ℃ for 3 min, (95 ℃ for 15 sec, 60 ℃ for 15 sec, 72 ℃ for 15 sec) X40 cycles.

When the efficiency of the wild type reverse transcriptase is 100%, compared with the reaction efficiency of the wild type reverse transcriptase, the reverse transcription efficiency of the mutant type reverse transcriptase is calculated by the following formula:

efficiency of reverse transcription 100%. times.2^(Ct _{Wild type} ^-Ct _{Mutant forms} ⁾

Wherein, the Random 6 Random primer sequence is as follows:

NNNNNN (N ═ A or T or G or C)

The GAPDH-PF primer sequence is as follows:

GCCTGCTTCACCACCTTCTT(SEQ ID NO.:3)

the GAPDH-PR primer sequence is as follows:

TGAACGGGAAGCTCACTGGC(SEQ ID NO.:4)

the M-MLV enzyme gene sequence of the present invention can be obtained by a conventional method used by those skilled in the art, for example, total artificial synthesis or PCR synthesis. One preferred synthesis method is the asymmetric PCR method. The asymmetric PCR method uses a pair of primers with different amounts to generate a large amount of single-stranded DNA (ssDNA) after PCR amplification. The pair of primers are referred to as non-limiting and limiting primers, respectively, and are typically in a ratio of 50-100: 1. In the first 10-15 cycles of the PCR reaction, the amplification product is mainly double-stranded DNA, but when the restriction primers (low concentration primers) are consumed, PCR using non-restriction primers (high concentration primers) will produce a large amount of single-stranded DNA. The primers used for PCR can be appropriately selected based on the sequence information of the present invention disclosed herein, and can be synthesized by a conventional method. The amplified DNA/RNA fragments can be isolated and purified by conventional methods, such as by gel electrophoresis.

The M-MLV enzyme mutant of the present invention can be expressed or produced by a conventional recombinant DNA technique, comprising the steps of:

(1) transforming or transducing a suitable host cell with a polynucleotide encoding a protein of the invention, or with a recombinant expression vector containing the polynucleotide;

(2) culturing the host cell in a suitable medium;

(3) separating and purifying the target protein from the culture medium or the cells to obtain the M-MLV enzyme mutant.

Methods well known to those skilled in the art can be used to construct expression vectors comprising a DNA sequence encoding the M-MLV enzyme of the invention and suitable transcription/translation control signals, preferably commercially available vectors: pET 28. These methods include in vitro recombinant DNA techniques, DNA synthesis techniques, in vivo recombinant techniques, and the like. The DNA sequence may be operably linked to a suitable promoter in an expression vector to direct mRNA synthesis. The expression vector also includes a ribosome binding site for translation initiation and a transcription terminator. In addition, the expression vector preferably comprises one or more selectable marker genes to provide a phenotypic trait for selection of transformed host cells.

The recombinant vector comprises in the 5 'to 3' direction: a promoter, a gene of interest, and a terminator. If desired, the recombinant vector may further comprise the following elements: a protein purification tag; a 3' polyadenylation signal; an untranslated nucleic acid sequence; transport and targeting nucleic acid sequences; selection markers (antibiotic resistance genes, fluorescent proteins, etc.); an enhancer; or operator.

Methods for preparing recombinant vectors are well known to those of ordinary skill in the art. The expression vector may be a bacterial plasmid, a bacteriophage, a yeast plasmid, a plant cell virus, a mammalian cell virus, or other vector. In general, any plasmid and vector may be used as long as it can replicate and is stable in the host.

One of ordinary skill in the art can construct vectors containing the promoter and/or gene sequence of interest of the present invention using well known methods. These methods include in vitro recombinant DNA techniques, DNA synthesis techniques, in vivo recombinant techniques, and the like.

The expression vector of the present invention can be used to transform an appropriate host cell so that the host transcribes the target RNA or expresses the target protein. The host cell may be a prokaryotic cell, such as E.coli, C.glutamicum, Brevibacterium flavum, Streptomyces, Agrobacterium: or lower eukaryotic cells, such as yeast cells; or higher eukaryotic cells, such as plant cells. It will be clear to one of ordinary skill in the art how to select an appropriate vector and host cell. Transformation of a host cell with recombinant DNA may be carried out using conventional techniques well known to those skilled in the art. When the host is a prokaryote (e.g., Escherichia coli), CaCl may be used₂The treatment can also be carried out by electroporation. When the host is a eukaryote, the following DNA transfection methods may be used: calcium phosphate coprecipitation, conventional mechanical methods (e.g., microinjection, electroporation, liposome encapsulation, etc.). The transformed plant may be transformed by methods such as Agrobacterium transformation or biolistic transformation, for example, leaf disc method, immature embryo transformation, flower bud soaking method, etc. The transformed plant cells, tissues or organs can be regenerated into plants by conventional methods to obtain transgenic plants.

The term "operably linked" means that the gene of interest to be expressed transcriptionally is linked to its control sequences in a manner conventional in the art to be expressed.

Culture of engineering bacteria and fermentation production of target protein

After obtaining the engineered cells, the engineered cells can be cultured under suitable conditions to express the protein encoded by the gene sequence of the invention. The medium used in the culture may be selected from various conventional media, depending on the host cell, and the culture is carried out under conditions suitable for the growth of the host cell. After the host cells have been grown to an appropriate cell density, the selected promoter is induced by suitable means (e.g., temperature shift or chemical induction) and the cells are cultured for an additional period of time.

In the present invention, conventional fermentation conditions may be employed. Representative conditions include (but are not limited to):

(a) the fermentation and induction temperature of the M-MLV enzyme is kept at 25-37 ℃ in terms of temperature;

(b) the pH value of the induction phase is controlled to be 3-9;

(c) in the case of Dissolved Oxygen (DO), DO is controlled at 10-90%, and the maintenance of dissolved oxygen can be solved by introducing oxygen/air mixed gas;

(d) for feeding, the feeding type preferably comprises carbon sources such as glycerol, methanol, glucose and the like, and the feeding can be carried out independently or in a mixed manner;

(e) as for the IPTG concentration during induction, conventional induction concentrations can be used in the present invention, and usually the IPTG concentration is controlled at 0.1-1.5 mM;

(f) the induction time is not particularly limited, and is usually 2 to 20 hours, preferably 5 to 15 hours.

The M-MLV enzyme of the target protein of the present invention exists in the cells of Escherichia coli, the host cells are collected by a centrifuge, and then the host cells are disrupted by high pressure, mechanical force, enzymatic cell disruption or other cell disruption methods to release the recombinant protein, preferably high pressure method. The host cell lysate can be primarily purified by flocculation, salting out, ultrafiltration, etc., and then purified by chromatography, ultrafiltration, etc., or directly purified by chromatography.

The chromatography includes cation exchange chromatography, anion exchange chromatography, gel filtration chromatography, hydrophobic chromatography, and affinity chromatography. Common chromatographic methods include:

1. anion exchange chromatography:

anion exchange chromatography media include (but are not limited to): Q-Sepharose, DEAE-Sepharose. If the salt concentration of the fermentation sample is higher, affecting binding to the ion exchange medium, the salt concentration needs to be reduced before ion exchange chromatography is performed. The sample can be replaced by means of dilution, ultrafiltration, dialysis, gel filtration chromatography and the like until the sample is similar to a corresponding ion exchange column equilibrium liquid system, and then the sample is loaded and subjected to gradient elution of salt concentration or pH.

2. Hydrophobic chromatography:

hydrophobic chromatographic media include (but are not limited to): Phenyl-Sepharose, Butyl-Sepharose, octyl-Sepharose. Samples were prepared by adding NaCl, (NH)₄)₂SO₄And increasing the salt concentration, loading, and eluting by decreasing the salt concentration. The hetero-proteins having large differences in hydrophobicity were removed by hydrophobic chromatography.

3. Gel filtration chromatography

Hydrophobic chromatographic media include (but are not limited to): sephacryl, Superdex, Sephadex types. The buffer system is replaced by gel filtration chromatography or further purified.

4. Affinity chromatography

Affinity chromatography media include (but are not limited to): HiTrap^TMHeparinHPColumns。

5. Membrane filtration

The ultrafiltration medium comprises: organic membranes such as polysulfone membranes, inorganic membranes such as ceramic membranes, metal membranes. The purification and concentration can be achieved by membrane filtration.

The main advantages of the invention are:

(1) the present invention provides a reverse transcriptase mutant which is resistant to high temperature and has high reverse transcription efficiency.

(2) The reverse transcriptase mutant with high reverse transcription efficiency is obviously improved in amplification efficiency compared with wild M-MLV enzyme under the same condition, so that the detection efficiency can be obviously improved.

(3) The invention screens 6 single-mutation high-temperature-resistant reverse transcriptase mutants from dozens of mutants in multiple rounds, and still can keep high reverse transcription efficiency at the reverse transcription temperature of 58 ℃. Moreover, 3 of the high-temperature resistant reverse transcriptase mutants can reach reaction equilibrium within 1 minute of reaction time. Therefore, each reverse transcriptase mutant obtained by screening has unexpected excellent technical effect.

(4) The single mutation site is combined to obtain the high-temperature resistant reverse transcriptase mutant containing multiple mutation sites, compared with the single mutation reverse transcriptase mutant, the reverse transcription efficiency of the high-temperature resistant reverse transcriptase mutant containing multiple mutation sites is further improved, and the combination of the dominant mutation sites is beneficial to improving the comprehensive performance of the M-MLV enzyme.

The present invention will be described in further detail with reference to the following examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Experimental procedures for conditions not specified in detail in the following examples are generally carried out under conventional conditions such as those described in molecular cloning, A laboratory Manual (Huang Petang et al, Beijing: scientific Press, 2002) by Sambrook. J, USA, or under conditions recommended by the manufacturer. Unless otherwise indicated, percentages and parts are by weight. The test materials and reagents used in the following examples are commercially available without specific reference.

Example 1 calculation and screening of DDG values at various sites

Inputting an MMLV protein sequence into Rosetta algorithm software Cyrus Bench (Cyrus Biotechnology), and calculating DDG values of all-site total mutation of 0-100, 101-200, 201-300, 301-400, 401-500, 501-600 and 601-671 amino acid segments to obtain mutation site information with the DDG values remarkably reduced (DDG values < -2), wherein the mutation site information comprises the following steps:

TABLE 1

Example 2 construction of MMLV mutant library

Based on the above protein sequences, DNA sequences were compiled by codon optimization from Cincisco, Suzhou, Inc. (SEQ ID No.: 2).

Gene synthesis was performed by Jinzhi Biotechnology Ltd, Suzhou according to the above DNA sequence, 5'(NheI) and 3' (XhoI) restriction sites were added, the gene was cloned into pET28a through 5'NheI and 3' XhoI to construct plasmid WT-pET28a, recombinant plasmid DNA and glycerol containing the recombinant plasmid were prepared, and site-directed mutagenesis was performed on plasmid WT-pET28a according to the mutation site referred to in example 1 to construct mutant pools Mu1-pET28a to Mu40-pET28 a.

Example 3 expression and purification of MMLV mutants

The plasmids WT-pET28a and Mu 1-40-pET 28a are transformed into BL21(DE3) competent cells to obtain 37 expression host bacteria, then the expression host bacteria are transferred into 3ml LB culture medium, shake culture is carried out for 5 hours at 37 ℃, and then 0.1Mm IPTG is added for induction culture overnight at 18 ℃. The induced cells were collected, lysed with lysis buffer (50Mm Tris, 50Mm NaCl, pH7.5), sonicated, and the supernatant was centrifuged. Taking supernatant, purifying by Ni NTA metal ion chelating filler to obtain wild type and 40 mutant MMLV proteins

EXAMPLE 4 screening of mutants

A: first round of screening (screening for mutations that retain Activity)

Wild type and 36 mutant MMLV proteins were reacted as above and inactivated at 42 ℃ for 15 min and 75 ℃ for 5 min. Then taking the reverse transcription product, and carrying out fluorescent quantitative PCR detection according to the following system

The results of the fluorescent quantitative PCR of the reverse transcription products of each mutant are shown in the following table:

TABLE 2

The underlined 14 mutants had ct values lower than the wild type, i.e., the reverse transcription efficiency was higher than the wild type. These mutants were selected for a second round of screening

B: second round of screening (screening for high temperature resistant mutation)

Selecting the mutant selected in the first round of screening, increasing the reverse transcription reaction temperature to 50 ℃, 55 and 58 ℃ according to the reverse transcription reaction system selected in the first round of screening, and then carrying out reverse transcription efficiency detection according to the fluorescent quantitative PCR system selected in the first round of screening, wherein the results are as follows:

TABLE 3

Remarking: when the efficiency of the wild type reverse transcriptase is 100%, compared with the reaction efficiency of the wild type reverse transcriptase, the reverse transcription efficiency of the mutant type reverse transcriptase is calculated by the following formula:

efficiency of reverse transcription ═ 100% × 2^(Ct _{Wild type} ^-Ct _{Mutant forms} ⁾

From the results of the second round of screening, Mu _15, 16, 26, 36, 38, 40, 6 mutants were reverse transcribed at 58 ℃ with an efficiency of not less than 50 ℃. These 6 mutants were selected for a third round of screening.

C: third round of screening (screening high Synthesis Rate mutations)

Selecting the mutant selected in the second round of screening, carrying out reverse transcription efficiency detection according to the reverse transcription reaction system selected in the first round of screening, the reverse transcription reaction temperature is 55 ℃, the reaction time is 1 minute, 2 minutes and 5 minutes, and then carrying out the reverse transcription efficiency detection according to the fluorescent quantitative PCR system selected in the first round of screening, wherein the results are as follows:

TABLE 4

Group of	1min/ct mean	2min/ct mean	5min/ct mean
				WT	24.88	22.99	21.85
15	22.24	20.28	19.17
				16	20.01	19.25	19.47
26	21.17	20.79	17.72
				36	17.64	17.92	17.93
38	21.15	20.73	20.14
				40	18.95	19.00	18.34

From the results of the third round of screening, the Mu _16, 36 and 40 reverse transcription reactions did not differ much from the reaction at 1 minute to 5 minutes, demonstrating that the reaction reached equilibrium after 1 minute of reaction.

Example 5

In the above example, 6 mutant sites capable of obtaining high temperature resistance and high activity of M-MLV enzyme were selected as follows:

in this example, the above 6 mutation sites are combined to construct 10 MMLV mutants, and it is expected that MMLV mutants having better performance than the above 6 single point mutations are obtained.

Mutations were made on the wild-type MMLV protein sequence according to the mutation site design in the table below.

The sequence of the wild-type MMLV protein is shown in SEQ ID NO. 1.

Based on the above protein sequences, DNA sequences were compiled by codon optimization of Jinzhi Biotech, Suzhou, with the wild-type MMLV DNA sequence (WT) as shown in SEQ ID No.: 2.

Gene synthesis was performed by Jinzhi Biotech Ltd, Suzhou according to the above DNA sequence, 5'(NheI) and 3' (XhoI) restriction sites were added, the gene was cloned into pET28a through 5'NheI and 3' XhoI, a plasmid WT-pET28a was constructed, recombinant plasmid DNA and glycerol containing the recombinant plasmid were prepared, and site-directed mutagenesis was performed on WT-pET28a according to the mutation sites concerned, and mutation pools Mu41-pET28a to Mu50-pET28a were constructed

Example 6 expression and purification of MMLV mutants

Mu 41-Mu 50-pET28a plasmids are transformed into BL21(DE3) competent cells to obtain 37 expression host bacteria, and then the expression host bacteria are transferred into 3ml LB culture medium, shake culture is carried out for 5 hours at 37 ℃, and then 0.1Mm IPTG18 ℃ is added for induction culture overnight. The induced cells were collected, lysed with lysis buffer (50Mm Tris, 50Mm NaCl, pH7.5), sonicated, and the supernatant was centrifuged. Taking supernatant, purifying by Ni NTA metal ion chelating filler to obtain 10 mutant MMLV proteins

Example 710 comparison of Heat resistance of mutant enzymes with Single Point mutant MMLV

200U/ul of 6 MMLV mutant enzyme proteins including Mu 41-Mu 5010 and Mu _15, 16, 26, 36, 38 and 40 were treated in a thermostatic metal bath at 50 ℃ for 60 minutes while heating at 50 ℃, 55 ℃, 60 ℃, 65 ℃ and 70 ℃ for 15 minutes, and then subjected to reverse transcription together with the enzyme sample which had not been subjected to the treatment. Extracting total RNA from Hela cells as a template, and carrying out reverse transcription reaction in the following system:

inactivation was carried out at 42 ℃ for 15 minutes and at 95 ℃ for 5 minutes. Then taking the reverse transcription product, and carrying out fluorescent quantitative PCR detection according to the following system

The results of the fluorescent quantitative PCR (Ct values) are shown in the following table:

from the above results, it can be seen that Mu _40 to Mu _50 of the combinatorial mutations are more stable than the single-site mutants at temperatures above 55 ℃. The reverse transcription performance of the enzyme was not substantially changed by treatment at 50 ℃ for 1 hour.

Example 810 comparison of the reaction rates of mutant enzymes with Single Point mutant MMLV

The reverse transcription reaction was carried out at 55 ℃ for 30 seconds, 1 minute, 2 minutes and 3 minutes, and the reverse transcription product was subjected to the fluorescent quantitative PCR assay in the same manner as in example 3. Ct values results are as follows:

as can be seen from the above results, the ct values of Mu _42, Mu _45, Mu _47, Mu _48, and Mu _49 after 1 minute of reaction were almost the same as those of 2 and 3 minutes of reaction, and therefore, it was judged that the equilibrium was reached after 1 minute of reaction. The ct values of the 10 combined mutants under the same reaction time are all smaller than those of single-point mutants, and the combination of the dominant mutation sites is proved to be beneficial to improving the comprehensive performance of the M-MLV enzyme.

Example 9 application to detection of nucleic acids of novel coronaviruses

The example provides the application of the screened combinatorial mutant M-MLV enzyme in a novel coronavirus (2019-nCoV) detection reagent.

The sequences of ORF1ab gene and N gene of 2019-nCoV virus are detected by fluorescent quantitative PCR method, and the sequence information of the used primers and probes is as follows:

Target 1(ORF1ab):

forward primer (F): CCCTGTGGGTTTTACACTTAA (SEQ ID NO. 5)

Reverse primer (R): ACGATTGTGCATCAGCTGA (SEQ ID NO. 6)

Fluorescent probe (P): 5'-FAM-CCGTCTGCGGTATGTGGAAAGGTTATGG-BHQ1-3' (SEQ ID NO: 7)

Target 2(N):

Forward primer (F): GGGGAACTTCTCCTGCTAGAAT (SEQ ID NO. 8)

Reverse primer (R): CAGACATTTTGCTCTCAAGCTG (SEQ ID NO. 9)

Fluorescent probe (P): 5'-FAM-TTGCTGCTGCTTGACAGATT-TAMRA-3' (SEQ ID NO: 10)

The reaction system is prepared as follows:

after the reaction system is prepared, RT-PCR is carried out as follows: 5 min at 55 ℃,2 min at 95 ℃ (30 sec at 95 ℃; fluorescence reading 1 min at 68 ℃) x 40 cycles. The results are as follows:

comparing the Ct difference (delta Ct) between the 5 combined mutant enzyme and the wild type M-MLV enzyme, calculating the difference multiple of the amplification efficiency of ORF1ab and N gene between the combined mutant enzyme and the wild type M-MLV enzyme as follows:

from the amplification Ct values of different combinations of mutant MMLV and wild type M-MLV enzyme on a new crown reference sample, the amplification efficiency of the mutant is obviously improved compared with that of the wild type.

All documents referred to herein are incorporated by reference into this application as if each were individually incorporated by reference. Furthermore, it should be understood that various changes and modifications of the present invention can be made by those skilled in the art after reading the above teachings of the present invention, and these equivalents also fall within the scope of the present invention as defined by the appended claims.

Sequence listing

<110> Daan Gen-Shaw Co Ltd of Zhongshan university

<120> reverse transcriptase and reverse transcription detection reagent

<130> 0000757

<160> 10

<170> SIPOSequenceListing 1.0

<210> 1

<211> 671

<212> PRT

<213> Murine leukemia Virus (Murine leukemia virus)

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Thr Leu Asn Ile Glu Asp Glu His 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 Ser 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 Thr Leu Gly Asn 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 Gln 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 Met

305 310 315 320

Ala Ala Pro Leu Tyr Pro Leu Thr Lys Thr Gly Thr Leu Phe Asn Trp

325 330 335

Gly Pro Asp Gln Gln Lys Ala Tyr Gln Glu Ile Lys Gln Ala Leu Leu

340 345 350

Thr Ala Pro Ala Leu Gly Leu Pro Asp Leu Thr Lys Pro Phe Glu Leu

355 360 365

Phe Val Asp Glu Lys Gln Gly Tyr Ala Lys Gly Val Leu Thr Gln Lys

370 375 380

Leu Gly Pro Trp Arg Arg Pro Val Ala Tyr Leu Ser Lys Lys Leu Asp

385 390 395 400

Pro Val Ala Ala Gly Trp Pro Pro Cys Leu Arg Met Val Ala Ala Ile

405 410 415

Ala Val Leu Thr Lys Asp Ala Gly Lys Leu Thr Met Gly Gln Pro Leu

420 425 430

Val Ile Leu Ala Pro His Ala Val Glu Ala Leu Val Lys Gln Pro Pro

435 440 445

Asp Arg Trp Leu Ser Asn Ala Arg Met Thr His Tyr Gln Ala Leu Leu

450 455 460

Leu Asp Thr Asp Arg Val Gln Phe Gly Pro Val Val Ala Leu Asn Pro

465 470 475 480

Ala Thr Leu Leu Pro Leu Pro Glu Glu Gly Leu Gln His Asn Cys Leu

485 490 495

Asp Ile Leu Ala Glu Ala His Gly Thr Arg Pro Asp Leu Thr Asp Gln

500 505 510

Pro Leu Pro Asp Ala Asp His Thr Trp Tyr Thr Asp Gly Ser Ser Leu

515 520 525

Leu Gln Glu Gly Gln Arg Lys Ala Gly Ala Ala Val Thr Thr Glu Thr

530 535 540

Glu Val Ile Trp Ala Lys Ala Leu Pro Ala Gly Thr Ser Ala Gln Arg

545 550 555 560

Ala Glu Leu Ile Ala Leu Thr Gln Ala Leu Lys Met Ala Glu Gly Lys

565 570 575

Lys Leu Asn Val Tyr Thr Asp Ser Arg Tyr Ala Phe Ala Thr Ala His

580 585 590

Ile His Gly Glu Ile Tyr Arg Arg Arg Gly Leu Leu Thr Ser Glu Gly

595 600 605

Lys Glu Ile Lys Asn Lys Asp Glu Ile Leu Ala Leu Leu Lys Ala Leu

610 615 620

Phe Leu Pro Lys Arg Leu Ser Ile Ile His Cys Pro Gly His Gln Lys

625 630 635 640

Gly His Ser Ala Glu Ala Arg Gly Asn Arg Met Ala Asp Gln Ala Ala

645 650 655

Arg Lys Ala Ala Ile Thr Glu Thr Pro Asp Thr Ser Thr Leu Leu

660 665 670

<210> 2

<211> 2013

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 2

acgctgaata tcgaggacga acaccgtctg cacgaaacca gcaaggagcc ggacgttagt 60

ctgggtagca cgtggctgag cgattttcca caagcgtggg cggaaaccgg tggtatgggt 120

ctcgccgttc gccaagcccc actcattatc ccactgaaag ccacgagcac gccggtgagc 180

atcaagcagt acccgatgag ccaagaagcc cgcctcggca ttaaaccgca tattcagcgt 240

ctgctggacc aaggcattct ggtgccgtgc cagagtccgt ggaatacgcc actgctcccg 300

gttaagaagc cgggcaccaa cgattatcgc ccggttcaag acctccgcga agtgaacaag 360

cgcgtggaag atatccatcc gaccgtgcca aatccgtaca atctgctgag tggcctcccg 420

ccgagtcatc aatggtacac cgtgctggat ctcaaggatg cgtttttctg cctccgtctg 480

catccaacca gccagccact ctttgcgttt gagtggcgcg acccagaaat gggtatcagc 540

ggtcaactga cgtggacgcg tctgccgcaa ggcttcaaaa acagcccgac gctgttcgat 600

gaggccctcc atcgcgatct ggcggatttc cgtatccagc atccagatct gattctgctg 660

cagtacgttg acgatctgct cctcgcggcc accagtgaac tggattgcca gcaaggtacc 720

cgtgcgctgc tgcagacgct gggcaatctg ggctaccgtg ccagcgcgaa aaaggcgcaa 780

atctgccaga agcaagttaa gtacctcggt tatctgctga aagagggtca acgctggctg 840

accgaggcgc gtaaagagac cgttatgggt cagccaacgc caaagacgcc acgccagctc 900

cgcgaatttc tgggtaccgc cggcttctgt cgtctgtgga ttccgggctt cgcggaaatg 960

gcggcgccac tctacccgct gaccaaaacc ggtaccctct tcaattgggg cccagatcag 1020

cagaaggcct accaagaaat taaacaagcg ctgctcaccg cgccggccct cggtctccca 1080

gatctgacca aaccgtttga gctgttcgtg gacgagaagc aaggctacgc caaaggcgtg 1140

ctgacccaga aactcggtcc atggcgtcgt ccggtggcct acctcagtaa gaaactggat 1200

ccagttgcgg cgggttggcc gccatgtctc cgtatggtgg cggcgattgc cgttctgacc 1260

aaagacgccg gcaaactcac catgggtcag ccgctggtta ttctcgcccc acatgcggtg 1320

gaagcgctgg ttaaacaacc gccagaccgc tggctgagca atgcccgcat gacccattat 1380

caagcgctgc tgctggacac cgaccgcgtt cagttcggtc cggtggttgc gctgaatcca 1440

gcgacgctgc tgccgctgcc agaagaaggt ctgcagcaca actgtctgga cattctggcc 1500

gaggcccatg gcacccgtcc agatctcacc gatcagccac tgccagacgc cgatcatacg 1560

tggtacaccg atggtagtag tctgctgcaa gaaggtcaac gtaaagcggg tgccgcggtg 1620

acgacggaaa ccgaggtgat ctgggccaaa gcgctgccag cgggtaccag cgcgcaacgt 1680

gcggaactga tcgcgctgac ccaagcgctc aaaatggccg agggcaagaa actcaacgtg 1740

tacaccgaca gtcgctacgc gtttgcgacc gcgcacatcc acggtgagat ttatcgccgc 1800

cgtggtctgc tcacgagcga aggtaaggag atcaagaata aggacgagat cctcgcgctg 1860

ctgaaagccc tctttctgcc gaaacgtctg agcatcatcc attgcccggg tcaccagaag 1920

ggccacagtg cggaagcgcg cggtaatcgc atggccgatc aagccgcgcg caaagcggcg 1980

attacggaaa ccccggatac gagcacgctg ctg 2013

<210> 3

<211> 20

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 3

gcctgcttca ccaccttctt 20

<210> 4

<211> 20

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 4

tgaacgggaa gctcactggc 20

<210> 5

<211> 21

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 5

ccctgtgggt tttacactta a 21

<210> 6

<211> 19

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 6

acgattgtgc atcagctga 19

<210> 7

<211> 28

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 7

ccgtctgcgg tatgtggaaa ggttatgg 28

<210> 8

<211> 22

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 8

ggggaacttc tcctgctaga at 22

<210> 9

<211> 22

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 9

cagacatttt gctctcaagc tg 22

<210> 10

<211> 20

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 10

ttgctgctgc ttgacagatt 20

Claims

1. An M-MLV enzyme mutant is characterized in that the amino acid residue position 313 and the amino acid residue position 607 of the M-MLV enzyme mutant are mutated, the amino acid residue position 313 is mutated into Gln, the amino acid residue position 607 is mutated into Lys, and the numbering of the amino acid residues corresponds to the numbering shown in SEQ ID NO. 1.

2. The M-MLV enzyme mutant of claim 1, wherein the amino acid sequence of the M-MLV enzyme mutant has at least about 80% homology to SEQ ID No. 1; more preferably, at least about 90% homologous; most preferably, at least about 95% homology; such as at least about 96%, 97%, 98%, 99% homology.

3. A polynucleotide molecule encoding the M-MLV enzyme mutant of claim 1.

4. A vector comprising the polynucleic acid molecule of claim 3.

5. A host cell comprising the vector or chromosome of claim 4 integrated with the polynucleic acid molecule of claim 3.

6. The host cell of claim 5, wherein the host cell is a prokaryotic cell or a eukaryotic cell.

7. A kit comprising the M-MLV enzyme mutant of claim 1.

8. A method of preparing the M-MLV enzyme mutant of claim 1, comprising the steps of:

(i) culturing the host cell of claim 5 under suitable conditions to express said M-MLV enzyme mutant; and

(ii) isolating said M-MLV enzyme mutant.

9. Use of the M-MLV enzyme mutant of claim 1 in the preparation of a reverse transcription detection reagent or a reverse transcription kit.

10. A method of reverse transcription of RNA, said method comprising the steps of:

(1) providing a sample containing RNA;

(2) reverse transcription reaction:

performing a reverse transcription reaction on the RNA-containing sample provided in step (1) using the reverse transcriptase mutant of claim 1.