JPWO2016084879A1 - Nucleic acid amplification reagent - Google Patents

Abstract

To provide a PCR reaction composition that has a high success rate in DNA replication, ie, high reaction specificity and amplification efficiency. By adding betaine to the reaction system using DNA polymerase belonging to family B and PCNA, it is possible to amplify long-chain target DNA and target DNA having a high GC ratio, and also to a reaction system containing an inhibitor. It was found that simple PCR is possible.

Description

The present invention relates to a nucleic acid amplification reagent used for PCR (polymerase chain reaction) excellent in reaction specificity and amplification efficiency.

PCR is (1) DNA denaturation by heat treatment (dissociation from double-stranded DNA to single-stranded DNA), (2) annealing of primer to template single-stranded DNA, (3) the primer using DNA polymerase This is a method of amplifying a target nucleic acid in a sample by repeating this cycle with 3 steps of the extension of 1 as one cycle. The target nucleic acid can be amplified hundreds of thousands of times even from a small amount of sample such as several copies, and it is widely used not only in the research field but also in the forensic field such as genetic diagnosis and clinical diagnosis, or in microbial testing in food and the environment. It has come to be used.

In PCR, reaction specificity and amplification efficiency are important. Here, the reaction specificity is the ability to specifically amplify only the target DNA. If the reaction specificity is low, non-specific amplification or primer dimer occurs, and the amplification amount of the target product decreases. It leads to things. The amplification efficiency refers to the efficiency of amplifying the target DNA. An ideal PCR with an amplification efficiency of 100% amplifies the target DNA twice in one cycle. If the amplification efficiency is low, the amount of target DNA amplified in one cycle decreases, resulting in a decrease in the amount of product obtained and the detection of the amplified target DNA.

Various PCR compositions have been studied to increase reaction specificity and amplification efficiency. For example, salts such as KCl, NH ₄ Cl, (NH ₄ ) ₂ SO ₄ , and tetramethylammonium hydroxide have a function of regulating the annealing power of the primer, and the optimum of these concentrations improves the reaction specificity and amplification efficiency. It becomes important to increase. In addition, additives such as betaine, glycerol, glycols, and sugars are said to prevent primer misannealing and to stabilize proteins, which can increase reaction specificity and amplification efficiency. Become.

As an additive for PCR, addition of a protein factor that works in cooperation with DNA polymerase as a replication factor has been studied. Single stranded binding protein (SSB) has been shown to specifically bind to single strands and destabilize the double helix structure of nucleic acids, thus preventing primer misannealing. Moreover, it has been shown that PCNA that works as a DNA clamp can be added to prevent dissociation of polymerase from a synthetic nucleic acid and increase amplification efficiency (Patent Document 1).

The DNA polymerase that performs PCR is also very important for improving reaction specificity and amplification efficiency. In general-purpose Taq DNA polymerase and Tth DNA polymerase, various mutations have been studied in order to improve PCR efficiency and reaction specificity. In addition, there is a DNA polymerase in which SSB is fused in order to increase the binding force with a nucleic acid. Recently, it has also been shown that DNA polymerase belonging to family B has higher amplification efficiency than DNA polymerase belonging to family A (general-purpose Taq DNA polymerase, Tth DNA polymerase, etc.). .

Patent Document 2 discloses a composition containing betaine in nucleic acid amplification using a DNA polymerase belonging to Family B, and suggests that various additives are used to enhance PCR performance. . However, even in the invention described in Patent Document 2, it is difficult to say that sufficient required characteristics are satisfied from the viewpoint of versatility.

In spite of various investigations as described above, it is found that PCR is not sufficiently amplified. In particular, amplification is difficult in DNA amplification of a long-chain target or a target having a region with a high GC ratio, and the reaction is inhibited even under conditions containing impurities, and DNA amplification may not occur. There is a need for a PCR composition that can efficiently amplify even under such difficult conditions (high reaction specificity and high amplification efficiency; the same applies hereinafter).

International Publication No. 2007/004654 Pamphlet JP 2010-213689 A

Carol J.H. Bull et al., Science 273, 1996, 1058-1073.

An object of the present invention is to provide a reaction composition having a high success rate in DNA replication. Still another object of the present invention is to provide a nucleic acid amplification reagent suitable for the above-mentioned purpose. In summary, an object of the present invention is to provide a PCR reaction reagent suitable for amplification of a gene in the presence of a base analog.

The nucleic acid amplification reagent of the present invention for achieving the above object is characterized by using DNA polymerase belonging to family B, PCNA, and betaine.

That is, as a result of intensive investigations in view of the above circumstances, the present inventors have further added betaine to a reaction system using a DNA polymerase belonging to Family B and PCNA, whereby a long chain target DNA or a region having a high GC ratio is obtained. It has been found that efficient PCR can be performed even in a reaction system containing a target DNA having an inhibitor and an inhibitory substance, and the present invention has been completed. The representative present invention is as follows.

[Claim 1]
A nucleic acid amplification reagent comprising DNA polymerase belonging to family B, Proliferating Cell Nuclear Antigen (PCNA), and betaine, wherein the PCNA consists of any of the following (1) or (2) Nucleic acid amplification reagent characterized.
(1) A polypeptide comprising an amino acid sequence in which one to several amino acid residues are substituted, deleted, inserted or added in the amino acid sequence shown in SEQ ID NO: 13, and having DNA polymerase amplification enhancing activity ( 2) A polypeptide comprising an amino acid sequence having a homology with the amino acid sequence of SEQ ID NO: 13 of 80% or more and having DNA polymerase amplification enhancing activity [Claim 2]
A nucleic acid amplification reagent comprising a DNA polymerase belonging to family B, PCNA and betaine, wherein the PCNA consists of any of the following (1) or (2):
(1) A polypeptide comprising an amino acid sequence in which one to several amino acid residues are substituted, deleted, inserted or added in the amino acid sequence shown in SEQ ID NO: 14 and having DNA polymerase amplification enhancing activity ( 2) A polypeptide comprising an amino acid sequence having a homology with the amino acid sequence of SEQ ID NO: 14 of 80% or more and having DNA polymerase amplification enhancing activity [Claim 3]
A nucleic acid amplification reagent comprising a DNA polymerase belonging to family B, PCNA and betaine, wherein the PCNA consists of any of the following (1) or (2):
(1) A polypeptide comprising an amino acid sequence in which one to several amino acid residues are substituted, deleted, inserted or added in the amino acid sequence shown in SEQ ID NO: 19, and having a DNA polymerase amplification enhancing activity ( 2) A polypeptide comprising an amino acid sequence having a homology with the amino acid sequence of SEQ ID NO: 19 of 80% or more and having DNA polymerase amplification enhancing activity [Claim 4]
Item 4. The nucleic acid amplification reagent according to any one of Items 1 to 3, wherein the DNA polymerase belonging to Family B is a DNA polymerase derived from Archaea.
[Section 5]
Item 5. The nucleic acid amplification reagent according to any one of Items 1 to 4, wherein the DNA polymerase belonging to Family B is an archaeal DNA polymerase mutant having reduced base analog detection activity.
[Claim 6]
Item 6. The nucleic acid amplification reagent according to any one of Items 1 to 5, wherein the DNA polymerase belonging to Family B has at least one amino acid modification in any of the amino acids constituting the 3′-5 ′ exonuclease active region.
[Claim 7]
Item 7. The nucleic acid amplification reagent according to any one of Items 1 to 6, wherein the PCNA is a mutant PCNA having amplification enhancing activity.

The present invention provides a PCR composition having excellent reaction specificity and amplification efficiency in DNA amplification. It can be widely used not only in the research field, but also in the clinical field such as genetic diagnosis or the field of forensic medicine, or in the examination of microorganisms in food or the environment.

Amplification of long target DNA Amplification of target DNA with high GC ratio DNA amplification from plant lysates The figure which shows the amino acid region regarding multimer formation of PCNA

Hereinafter, it demonstrates further in detail, showing embodiment of this invention.
In this specification, the base sequence, the amino acid sequence, and individual constituent elements thereof may be simplified symbols using single-letter alphabets, but all follow the practices in the fields of molecular biology and genetic engineering. Further, in this specification, in order to simply show the mutation of the amino acid sequence, for example, a notation such as “D143A” is used. “D143A” indicates that the 143rd aspartic acid was substituted with alanine, that is, the type of amino acid residue before substitution, its location, and the type of amino acid residue after substitution. Further, the sequence numbers correspond to the sequence numbers described in the sequence listing unless otherwise specified. In the case of multiple mutants, the above notation is connected by “/”. For example, “D143A / D147A” indicates that the 143rd aspartic acid was substituted with alanine and the 147th aspartic acid was substituted with alanine. For multiple mutants of the triple mutant or more, information on the mutation site such as “P36H” is added after the symbol “/”. In the present specification, the term “mutant” in the case of “mutant PCNA” means that it has an amino acid sequence different from the conventionally known PCNA, and is caused by artificial mutation or natural variation. It does not distinguish whether or not.

(1) Nucleic acid amplification reagent One of the embodiments of the present invention is a reagent for amplifying a nucleic acid,
(A) DNA polymerase belonging to family B, and (b) PCNA
(C) A nucleic acid amplification reagent which performs a DNA synthesis reaction in the presence of betaine.

(1.1)
The nucleic acid amplification reagent in the present invention is not particularly limited as long as it can be amplified by a DNA polymerase. PCR is a typical nucleic acid amplification method, but the nucleic acid amplification reagent of the present invention is not only PCR, but also a primer by reacting one kind of primer, dNTP (deoxyribonucleotide triphosphate), using DNA as a template. Can also be used to synthesize DNA primer extensions. Specifically, a primer extension method, a sequencing method, a conventional method that does not perform temperature cycling, a cycle sequence method, and the like are included.

The nucleic acid applied to the nucleic acid amplification reagent of the present invention is not particularly limited as long as it can be amplified by DNA polymerase, and is not limited by its length, sequence, GC content, or the like. Typically, the nucleic acid is DNA composed of adenine (A), cytosine (C), guanine (G), and thymine (T). However, in the nucleic acid amplification reagent of the present invention, the nucleic acid is “decreased”. In this specification, it is possible to use a mutant having a detection activity ”(bases other than adenine, cytosine, guanine, and thymine are referred to as base analogs). Therefore, adenine, cytosine, guanine, thymine Other bases such as uracil and inosine may be included. Hereinafter, in the present specification, unless otherwise specified, the base constituting the DNA may include any of the above A, C, G, T, and base analogs.

In the nucleic acid amplification reagent of the present invention, a typical composition in the case of PCR is shown below, but is not limited thereto. For example, the amplification target DNA
(A) DNA polymerase belonging to family B (b) PCNA
(C) Besides betaine,
(D) a pair of primers in which one primer is complementary to the DNA extension product of the other primer (e) a DNA synthesis substrate (deoxynucleotide triphosphate (dNTP)), and
(F) mixing a buffer solution containing magnesium ions, ammonium ions and / or potassium ions,
By using a thermal cycler or the like to raise or lower the temperature of the reaction solution in the cycles shown in (I) to (IV) below, (1) DNA denaturation, (2) primer annealing, and (3) primer extension Repeat thermal cycling to amplify specific DNA fragments.
(I) The reaction solution is heated to about 94 ° C., and the temperature is maintained for 30 seconds to 1 minute to separate the double-stranded DNA into single strands.
(II) Rapid cooling to about 60 ° C. (slightly different depending on the primer), and annealing the single-stranded DNA and the primer.
(III) Heat again to a temperature range that is optimal for DNA polymerase activity without primer separation. Depending on the experimental purpose, the temperature is set to about 60-72 ° C. This temperature is usually maintained for 1 to 2 minutes depending on the time required for DNA synthesis and the length of amplification.
(IV) This is one cycle, and thereafter, the procedure from (I) to (III) is repeated to amplify a specific DNA fragment.

In the PCR, BSA and a nonionic surfactant may be further used as necessary. Furthermore, an antibody having the activity of suppressing the polymerase activity and / or 3'-5 'exonuclease activity of the thermostable DNA polymerase may be used. Examples of the antibody include a monoclonal antibody and a polyclonal antibody. This reaction composition is particularly effective for increasing the sensitivity of PCR and reducing nonspecific amplification.

(1.2)
[DNA polymerase belonging to family B]
The DNA polymerase used in the nucleic acid amplification reagent of the present invention is a DNA polymerase belonging to Family B. In the present invention, the DNA polymerase belonging to Family B refers to a DNA polymerase having 3′-5 ′ exonuclease activity and not having 5′-3 ′ exonuclease activity. A DNA polymerase derived from archaea (Archia) is preferred. The DNA polymerase belonging to the family B is preferably an archaea-derived DNA polymerase.

[A DNA polymerase derived from archaea]
Examples of DNA polymerases derived from archaea belonging to family B include DNA polymerases isolated from bacteria of the genus Pyrococcus and Thermococcus. Examples of the DNA polymerase derived from the genus Pyrococcus include Pyrococcus furiosus and Pyrococcus sp. Including, but not limited to, DNA polymerases isolated from GB-D, Pyrococcus Wosei, Pyrococcus abyssi, Pyrococcus horikoshii. Examples of DNA polymerases derived from the genus Thermococcus include Thermococcus kodakaraensis, Thermococcus gorgonarius, Thermococcus litoralis, Thermococcus sp. JDF-3, Thermococcus sp. 9 degrees North-7 (Thermococcus sp. 9 ° N-7), Thermococcus sp. Including, but not limited to, DNA polymerase isolated from KS-1, Thermococcus celler, or Thermococcus sicili. These DNA polymerases are commercially available: Pfu (Staragene), KOD (Toyobo), Pfx (Life Technologies), Vent (New England Biolabs), Deep Vent (New England Biolabs), Tgo (Ro), Tgo (Rw) and so on. Among these, from the viewpoint of PCR efficiency, KOD DNA polymerase excellent in extensibility and thermal stability is preferable.

Moreover, you may use the variant which gave the modification | change which has the modification | change of the below-mentioned 3'-5 'exonuclease area | region and / or the reduced base analog detection activity to the said DNA polymerase.

(1.3)
[Modification of DNA polymerase (I) Modification of 3′-5 ′ exonuclease region]
The modified DNA polymerase used in the nucleic acid amplification reagent of the present invention may further contain at least one amino acid modification in any of the amino acid sequences of the 3′-5 ′ exonuclease active region.

3'-5 'exonuclease activity refers to the ability to remove incorporated nucleotides from the 3' end of a DNA polymer, and the above 3'-5 'exonuclease region is a DNA polymerase belonging to family B. It is a highly conserved site, derived from Thermococcus kodakaraensis DNA polymerase (SEQ ID NO: 1), Pyrococcus furiosus DNA polymerase (SEQ ID NO: 2), Thermococcus gorgonarius DNA polymerase (SEQ ID NO: 3), DNA polymerase derived from Thermococcus litoralis (SEQ ID NO: 4), DNA polymerase derived from Pyrococcus sp GB-D (SEQ ID NO: 5), derived from Thermococcus sp JDF-3 DNA polymerase (SEQ ID NO: 6 DNA polymerase derived from Thermococcus sp 9 ° N-7 (SEQ ID NO: 7), DNA polymerase derived from Thermococcus sp KS-1 (SEQ ID NO: 8), DNA polymerase derived from Thermococcus cellar (sequence) In the DNA polymerase (SEQ ID NO: 10) derived from No. 9) or Thermococcus cyclis, the 137-147, 206-222, and 308-318th amino acids. In the present invention, the present invention is also applied to a DNA polymerase other than the DNA polymerase specifically presenting the sequence. In addition, in the archaeal DNA polymerase belonging to Family B other than the DNA polymerases shown in SEQ ID NOs: 1 to 10, 3′- consisting of amino acids 137 to 147, 206 to 222, and 308 to 318 of SEQ ID NO: 1 The region corresponding to the 5 ′ exonuclease region is shown.

The “amino acids corresponding to the 137th to 147th, 206th to 222nd, and 308th to 318th amino acids shown in SEQ ID NO: 1” are DNA polymerases having an amino acid sequence that is not completely identical to the amino acid sequence shown in SEQ ID NO: 1. This is an expression including amino acid sequences corresponding to positions 137 to 147, 206 to 222, and 308 to 318 of SEQ ID NO: 1. In this specification, the meaning of “corresponding” in the notation of the same format as described above is the same as in the above example.

In the present invention, in the amino acid sequence that is not completely identical to the amino acid sequence shown in SEQ ID NO: 1, a certain position (order) on SEQ ID NO: 1 and the corresponding amino acid position were compared (aligned) with the primary structure of the sequence. In this case, the position corresponds to the position of SEQ ID NO: 1. In the present specification, the meaning of “corresponding position” in the notation of the same format as described above is the same as the above example.

Various methods are known as methods for comparing the primary structures of sequences. For example, it can be calculated using an analysis tool that is commercially available or available through a telecommunication line (Internet). In the present invention, by using the default (initial setting) parameters in ClustalW (http://clustalw.ddbj.nig.ac.jp/index.php/lang=ja) of DNA Databank of Japan (DDBJ), Compare the primary structure of the sequences.

The modification of the 3'-5 'exonuclease region can be composed of substitution, deletion, or addition, but is not particularly limited. For example, modifications to amino acids corresponding to positions 137 to 147, 206 to 222, and 308 to 318 in SEQ ID NO: 1 are shown.

As the DNA polymerase in which the 3′-5 ′ exonuclease active region is modified, one in which at least one of amino acids corresponding to positions 141, 142, 143, 210, 311 in SEQ ID NO: 1 or SEQ ID NO: 2 is modified is preferable. . These modified DNA polymerases are deficient in 3'-5 'exonuclease activity. More preferably, it is a DNA polymerase deficient in 3'-5 'exonuclease activity, wherein the amino acid modification is any one selected from D141A, E143A, D141A / E143A, I142R, N210D, or Y311F. In addition, 3'-5 'exonuclease activity-deficient (exo (-)) DNA polymerase includes a complete lack of activity, for example, 0.03%, 0.05% compared to the parent enzyme , 0.1%, 1%, 5%, 10%, 20%, or at most 50% or less of a modified DNA polymerase having exonuclease activity.

Another preferred form of the DNA polymerase in which the 3'-5 'exonuclease active region is modified is any one selected from H147E and H147D in SEQ ID NO: 1 or SEQ ID NO: 2. These modified DNA polymerases have improved PCR efficiency while maintaining exonuclease activity.

A method for producing a DNA polymerase in which the 3′-5 ′ exonuclease active region is modified and a method for analyzing the 3′-5 ′ exonuclease activity are known and disclosed in, for example, US Pat. No. 6,946,273. Yes. A DNA polymerase with improved PCR efficiency refers to a modified DNA polymerase in which the amount of PCR product is increased compared to the parent enzyme. A method for analyzing whether or not the amount of the PCR product is increased as compared with the parent enzyme is described in Japanese Patent No. 3891330.

(1.4)
[Modification of DNA polymerase (II) Modification to produce a DNA polymerase mutant having reduced base analog detection activity]
The DNA polymerase belonging to family B used for the nucleic acid amplification reagent of the present invention may be a mutant having reduced base analog detection activity. Base analogs refer to bases other than adenine, cytosine, guanine, and thymine, and include uracil and inosine. Usually, a DNA polymerase belonging to Family B binds strongly when a base analog such as uracil or inosine is detected, and inhibits the polymerase function. The base analog detection activity refers to an activity that strongly binds to a base analog and inhibits the polymerase function. A DNA polymerase mutant belonging to family B having reduced base analog detection activity is a DNA polymerase mutant belonging to family B characterized by low binding ability to uracil and inosine.

Such a mutant can be prepared by modifying at least one position of the amino acid sequence (uracil binding pocket) relating to uracil binding. Specifically, uracil-binding pockets formed by archaebacterial DNA polymerase belonging to family B, for example, amino acid sequence (SEQ ID NO: 1) of DNA polymerase from Thermococcus kodakaraensis KOD1 strain (SEQ ID NO: 1) and 78-130 Examples include DNA polymerase mutants that have been modified at least at one site and have reduced ability to bind to uracil or inosine compared to wild-type DNA polymerase. DNA polymerase mutants with low binding ability to uracil and inosine do not show much decrease in DNA polymerase function even in PCR in the presence of dUTP, and the effect of dUTP on the elongation reaction of DNA polymerase is reduced.

The amino acid sequence for uracil binding is highly conserved in DNA polymerases derived from Pyrococcus and Thermococcus. In DNA polymerase (SEQ ID NO: 1) derived from Thermococcus kodakaraensis, it is formed by amino acids 1 to 40 and amino acids 78 to 130. In Pyrococcus furiosus (SEQ ID NO: 2), it is formed by amino acids 1 to 40 and amino acids 78 to 130. In Thermococcus gorgonarius (SEQ ID NO: 3), it is formed by amino acids 1 to 40 and amino acids 78 to 130. In Thermococcus litoralis (SEQ ID NO: 4), it is formed by amino acids 1 to 40 and amino acids 78 to 130. In Pyrococcus sp. GB-D (SEQ ID NO: 5), it is formed by amino acids 1 to 40 and amino acids 78 to 130. In Thermococcus sp. JDF-3 (sequence number 6), it is formed by amino acids 1-40 and amino acids 78-130. In Thermococcus sp 9 ° N-7 (SEQ ID NO: 7), it is formed by amino acids 1 to 40 and amino acids 78 to 130. In Thermococcus sp KS-1 (SEQ ID NO: 8), it is formed by amino acids 1-40 and amino acids 78-130. In Thermococcus cellar (SEQ ID NO: 9), it is formed by amino acids 1-40 and amino acids 78-130. In Thermococcus cyclis (SEQ ID NO: 10), it is formed by amino acids 1-40 and amino acids 78-130.

(1.5)
More preferred as a DNA polymerase mutant having reduced base analog detection activity for use in the nucleic acid amplification reagent of the present invention is assumed to be directly related to interaction with uracil 7, 36, 37, 90 -97, and archaeal DNA polymerase mutant in which at least one of amino acids 112 to 119 is modified, for example, (a) 7, 36, 37 of the amino acid sequence shown by SEQ ID NO: 1 or SEQ ID NO: 2 , 90-97 and 112-119th amino acids, archaebacterial DNA polymerase mutant represented by an amino acid sequence having at least one amino acid modification.

(1.6)
The DNA polymerase mutant may be one represented by the following amino acid sequence (b).
(B) In the amino acid sequence represented by (a), at least one amino acid is further modified at positions other than the 7, 36, 37, 90 to 97, and 112 to 119th positions. The identity or the identity between the amino acid sequence and SEQ ID NO: 2 is 80% or more (preferably 85% or more, more preferably 90% or more, further preferably 95% or more, more preferably 98%. An amino acid sequence encoding a DNA polymerase having a reduced base analog detection activity.

Various methods are known as methods for calculating the identity of amino acid sequences. For example, it can be calculated using an analysis tool that is commercially available or available through a telecommunication line (Internet). In the present invention, the National Biotechnology Information Center (NCBI) homology algorithm BLAST (Basic local alignment search tool) http: // www. ncbi. nlm. nih. The amino acid sequence identity is calculated by using default (initial setting) parameters in gov / BLAST /.

(1.7)
The DNA polymerase mutant may be one represented by the following amino acid sequence (c).
(C) In the amino acid sequence represented by (a), one or several amino acids are further deleted, substituted or added at sites other than the 7, 36, 37, 90 to 97, and 112 to 119 positions, and An amino acid sequence encoding a DNA polymerase having reduced base analog detection activity.

Here, “several” is not limited as long as “decreased base analog detection activity” is maintained, but is, for example, a number corresponding to less than about 20% of all amino acids, preferably less than about 15%. It is a corresponding number, more preferably a number corresponding to less than about 10%, even more preferably a number corresponding to less than about 5%, and most preferably a number corresponding to less than about 1%. More specifically, the number of amino acid residues to be mutated is, for example, 2 to 160, preferably 2 to 120, more preferably 2 to 80, still more preferably 2 to 40, and even more. Preferably it is 2-5.

The “amino acids corresponding to positions 7, 36, 37, 90 to 97, and 112 to 119 in the amino acid sequence shown in SEQ ID NO: 1” are amino acid sequences that are not completely identical to the amino acid sequence shown in SEQ ID NO: 1. In the DNA polymerase having the amino acid sequence, the amino acid sequence relating to the binding of uracil corresponding to positions 7, 36, 37, 90 to 97, and 112 to 119 of SEQ ID NO: 1.

In the present invention, a position (order) on SEQ ID NO: 1 in an amino acid sequence that is not completely identical to the amino acid sequence shown in SEQ ID NO: 1 is compared with a position corresponding to a position (sequence) on the primary structure of the sequence, The position corresponds to the position of SEQ ID NO: 1. In this specification, the meaning of “corresponding” in the notation of the same format as described above is the same as in the above example.

In the present invention, the position corresponding to a certain position (order) on SEQ ID NO: 6 in the amino acid sequence not completely identical to the amino acid sequence shown in SEQ ID NO: 1 is compared (aligned) with the primary structure of the sequence. The position corresponds to the position of SEQ ID NO: 1. In the present specification, the meaning of “corresponding position” in the notation of the same format as described above is the same as the above example.

Various methods are known as methods for comparing the primary structures of sequences. For example, it can be calculated using an analysis tool that is commercially available or available through a telecommunication line (Internet). In the present invention, by using the default (initial setting) parameters in ClustalW (http://clustalw.ddbj.nig.ac.jp/index.php/lang=ja) of DNA Databank of Japan (DDBJ), Compare the primary structure of the sequences.

(1.8)
The DNA polymerase mutant having reduced base analog detection activity used for the nucleic acid amplification reagent of the present invention is more preferably selected from at least amino acids corresponding to amino acids Y7, P36, or V93 in SEQ ID NO: 1 or SEQ ID NO: 2. Has one amino acid modification. Here, for example, Y7 means a tyrosine (Y) residue which is the seventh amino acid, and one letter of the alphabet represents an abbreviation of a commonly used amino acid. In a preferred example, the Y7 amino acid has tyrosine (Y) substituted with a nonpolar amino acid, specifically selected from the group consisting of Y7A, Y7G, Y7V, Y7L, Y7I, Y7P, Y7F, Y7M, Y7W, and Y7C. Amino acid substitution. In another preferred example, the P36 amino acid is substituted with a polar amino acid in which proline (P) is positively charged, specifically P36H, P36K, or P36R. In another preferred example, the V93 amino acid has a valine (V) substituted with a positively charged polar amino acid, specifically a V93H, V93K, or V93R amino acid substitution.

More preferably, the modification is at least one amino acid modification selected from the group consisting of Y7A, P36H, P36K, P36R, V93Q, V93K, and V93R. More preferably, it is P36K, P36R or P36H. Particularly preferred is P36H.

The DNA polymerase mutant having reduced base analog detection activity in the present invention is a modified version of two or more amino acids selected from amino acids corresponding to amino acids Y7, P36, or V93 in SEQ ID NO: 1 or SEQ ID NO: 2. But it ’s okay. Specific examples include Y7A / V93K, Y7A / P36H, Y7A / P36R, Y7A / V93R, Y7A / V93Q, or P36H / V93K, preferably Y7A / P36H or Y7A / V93K. It is not limited.

In addition, in patent 4395377 gazette or JP-T-2006-507012 gazette, the 7th, 36th, 37th, 90th to 97th, and 112th to 119th amino acids assumed to be directly related to the interaction with uracil. Several archaeal DNA polymerase mutants in which any of these are modified are exemplified. However, not all of the variants have good properties that can solve the problems of the present invention, and some of them have lost activity.

(1.9)
Based on the modification of the DNA polymerase exemplified above, various mutants can be considered as the modified DNA polymerase used in the nucleic acid amplification reagent of the present invention. Examples of such mutants include, but are not limited to, archaeal DNA polymerase mutants having any of the following modifications (1) to (4).
(1) (A) H147E and (B) Y7A / V93K, Y7A / V93R, Y7A / V93Q, Y7A / P36H, Y7A / P36R, P36H / V93K, P36K, P36R, P36H, V93R or V93Q (2 ) (A) N210D, (B) Y7A / V93K, Y7A / P36H, Y7A / P36R, P36K, P36R, P36H, V93Q, V93K or V93R (3) (A) I142R and (B) Y7A / V93K, Y7A / V93R, Y7A / V93Q, Y7A / P36H, Y7A / P36R, P36R, P36H, V93K, V93R, or V93Q (4) (A) D141A / E143A and (B) Y7A / V93K, Y7A / P36H, Y7A / P36R, P36R, P36H or V93 One of the

(1.10)
[Method for evaluating base analog detection activity]
The base analog detection activity in the present invention can be evaluated by PCR. The base analog is typically uracil. For example, a dUTP solution is added at a final concentration of 0.5 μM to 200 μM to a normal PCR reaction solution containing DNA as a template, buffer material, magnesium, dNTPs, primers, and a DNA polymerase to be evaluated, and thermal cycling is performed. After the reaction, the presence or absence of a PCR product is confirmed by ethidium bromide-stained 1% agarose electrophoresis, and the detection activity of uracil can be evaluated by the allowable dUTP concentration. A DNA polymerase having a high uracil detection activity inhibits the extension reaction when a little dUTP is added, and the PCR product cannot be confirmed. In addition, DNA polymerase with low uracil detection activity can confirm DNA amplification by PCR without problems even when a high concentration of dUTP is added.

A DNA polymerase mutant having reduced base analog detection activity means that there is no mutation as a result of optimal thermal cycling using any primer and DNA as a template in the enzyme optimal reaction buffer. Compared to the wild type, it refers to a DNA polymerase in which the elongation reaction is not inhibited even when a high concentration of dUTP is added, and the PCR product can be confirmed. However, when it is difficult to compare with wild type, archaeal DNA polymerase mutants that can be amplified by PCR even when dUTP is added at a concentration of 0.5 μM, the mutants are reduced compared to wild type. It is presumed to have the activity of detecting a base analog.

The evaluation of the base analog detection activity in the present invention follows the following method.
KOD-Plus-Ver. 2 (Toyobo) attached 10 × PCR Buffer or Pfu DNA Polymerase (Agilent) attached 10 × PCR Buffer, 1 × PCR Buffer, 1.5 mM MgSO ₄ , 0.2 mM dNTPs (dATP, dTTP, (dCTP, dGTP), 15 pmol of a primer described in SEQ ID NOS: 11 and 12 for amplifying about 1.3 kb, 10 ng of human genomic DNA (Roche Human Genomic DNA; model number 116111112001), in a 50 μl reaction solution containing 1 U of each enzyme DUTP (Roche) is added to a final concentration of 0.5, 5, 50, 100, and 200 μM. After the pre-reaction at 94 ° C. for 30 seconds, PCR is performed using PCR system GeneAmp 9700 (Applied Biosystem) with a schedule of repeating 98 cycles of 10 ° C., 10 seconds → 65 ° C., 30 seconds → 68 ° C., 1 minute 30 seconds. After completion of the reaction, 1% agarose electrophoresis is performed on 5 μl of the reaction solution, ethidium bromide staining is performed, and whether or not the base analog detection activity is decreased by confirming the amplified DNA fragment of about 1.3 kb under ultraviolet irradiation. Can be evaluated.

(1.11)
[Method of introducing amino acid modification]
A method for modifying a DNA polymerase used in the nucleic acid amplification reagent of the present invention has already been established in the art. Therefore, it can modify | change according to a well-known method, The aspect in particular is not restrict | limited.

As one embodiment of a method for introducing an amino acid modification, a site-directed mutagenesis method based on the inverse PCR method can be used. For example, KOD-Plus-Mutageness Kit (manufactured by Toyobo) (1) denatures a plasmid into which a target gene has been inserted, anneals a mutation primer to the plasmid, and subsequently performs an extension reaction using KOD DNA polymerase. (2) Repeat the cycle of (1) 15 times. (3) Selectively cleave only the plasmid as a template using the restriction enzyme DpnI. (4) Phosphorylation of newly synthesized gene, Ligation (5) A kit that can transform a cyclized gene into Escherichia coli and obtain a transformant having a plasmid introduced with the target mutation.

The modified DNA polymerase gene is transferred to an expression vector as necessary, and, for example, E. coli as a host is transformed with the expression vector, and then applied to an agar medium containing a drug such as ampicillin to form colonies. The colony is inoculated in a nutrient medium such as LB medium or 2 × YT medium and cultured at 37 ° C. for 12 to 20 hours, and then the cells are crushed and the crude enzyme solution is extracted. A vector derived from pBluescript is preferable. Any known method may be used as a method for crushing bacterial cells. For example, ultrasonic treatment, a physical crushing method such as French press or glass bead crushing, or a lytic enzyme such as lysozyme can be used. This crude enzyme solution is heat-treated at 80 ° C. for 30 minutes to inactivate the host-derived polymerase, and the DNA polymerase activity is measured.

Any method may be used as a method for obtaining purified DNA polymerase from the strain selected by the above method. For example, the following method is preferable. That is, after collecting cells obtained by culturing in a nutrient medium, a crude enzyme solution is obtained by crushing and extracting by enzymatic or physical crushing methods. The obtained crude enzyme extract is heat-treated, for example, at 80 ° C. for 30 minutes, and then the DNA polymerase fraction is recovered by ammonium sulfate precipitation. This crude enzyme solution can be desalted by a method such as gel filtration using Sephadex G-25 (manufactured by Amersham Pharmacia Biotech). After this operation, it can be separated and purified by heparin sepharose column chromatography to obtain a purified enzyme preparation. The purified enzyme preparation is purified by SDS-PAGE to such an extent that it shows an almost single band.

(1.12)
[Method for measuring DNA polymerase activity]
In the present invention, the DNA polymerase used for the nucleic acid amplification reagent measures activity as follows. If the enzyme activity is strong, the sample is stored in a storage buffer (50 mM Tris-HCl (pH 8.0), 50 mM KCl, 1 mM dithiothreitol, 0.1% Tween 20, 0.1% Nonidet P40, 50% glycerin). Dilute and measure.
(1) 25 μl of the following solution A, 5 μl of solution B, 5 μl of solution C, 10 μl of sterilized water, and 5 μl of enzyme solution are added to a microtube and reacted at 75 ° C. for 10 minutes. (2) Then, ice-cool, add 50 μl of E solution and 100 μl of D solution, and stir on ice for 10 minutes after stirring. (3) This solution is filtered through a glass filter (GF / C filter manufactured by Whatman) and thoroughly washed with 0.1N hydrochloric acid and ethanol. (4) The radioactivity of the filter is measured with a liquid scintillation counter (TriCarb 2810TR manufactured by PerkinElmer), and the incorporation of nucleotides into the template DNA is measured. One unit of enzyme activity is defined as the amount of enzyme that takes 10 nmol nucleotides per 30 minutes into the acid-insoluble fraction (that is, the fraction insolubilized when the solution D is added) under these conditions.
Solution A: 40 mM Tris-HCl buffer (pH 7.5), 16 mM magnesium chloride 15 mM dithiothreitol, 100 μg / mL BSA (bovine serum albumin)
Solution B: 1.5 μg / μl activated calf thymus DNA
Solution C: 1.5 mM dNTP (250 cpm / pmol [3H] dTTP)
Liquid D: 20% trichloroacetic acid (2 mM sodium pyrophosphate)
Solution E: 1 mg / mL calf thymus DNA

(2) PCNA
(2.1)
PCNA (Proliferating Cell Nuclear Antigen) used for the nucleic acid amplification reagent of the present invention is a kind of PCR enhancing factor. The PCNA is not particularly limited, but is preferably a heat-resistant one that can withstand the thermal cycle of PCR, and preferably one that remains active after PCR. More preferably, it is soluble even after heat treatment at 80 ° C. for 30 minutes, and the activity remains at 50% or more, more preferably at least 70%, particularly preferably at least 90%.

Examples of such PCNA include PCNA isolated from bacteria of the genus Pyrococcus and Thermococcus. PCNA derived from the genus Pyrococcus includes Pyrococcus furiosus (SEQ ID NO: 13), Pyrococcus sp. Including, but not limited to, PCNA isolated from GB-D, Pyrococcus Wosei, Pyrococcus abyssi or Pyrococcus horikoshii. PCNAs derived from the genus Thermococcus include Thermococcus kodakaaraensis (SEQ ID NO: 14), Thermococcus gonorarius, Thermococcus litoralis, Thermococcus sp. JDF-3, Thermococcus sp. 9 degrees North-7 (Thermococcus sp. 9 ° N-7), Thermococcus sp. KS-1, Thermococcus celer, or Thermococcus siculi, Methanococcus jannaschii (Mja) or Methanobacterium thermoautotropicum (Mth), including but not limited to PCNA.

A gene encoding PCNA can be cloned from an organism having PCNA. It can also be artificially synthesized based on amino acid sequence information and nucleic acid sequence information.

Furthermore, the PCNA used in the nucleic acid amplification reagent of the present invention may be a mutant that is loaded into DNA alone (having DNA polymerase amplification enhancing activity). PCNA usually forms a multimer and has a ring-like structure. Loading to DNA indicates that the DNA is allowed to pass inside the ring structure of the PCNA multimer, and PCNA can be loaded into DNA only in combination with a factor usually called RFC. Mutants that load DNA alone are those that modify the sites involved in PCNA multimer formation and destabilize multimer formation, making it easier to pass DNA into PCNA multimers without RFC. Show.

Specific examples of PCNA used in the nucleic acid amplification reagent of the present invention include the following. A polypeptide comprising an amino acid sequence in which one to several amino acid residues are substituted, deleted, inserted or added in the amino acid sequence described in SEQ ID NO: 13, 14 or 19, and having DNA polymerase amplification enhancing activity It is. Further, it may be a polypeptide comprising an amino acid sequence having 80% or more homology with the amino acid sequence described in SEQ ID NO: 13, 14, or 19 and having DNA polymerase amplification enhancing activity. More preferably, the homology with the amino acid sequence shown in SEQ ID NO: 13, 14 or 19 is 85% or more, more preferably 88% or more, still more preferably 90% or more, still more preferably 93% or more, even more Preferably it is 95% or more, Especially preferably, it is 98% or more, Most preferably, it is 99% or more. Such a polypeptide comprising an amino acid sequence having a certain identity or more can be prepared based on the known genetic engineering techniques as described above.

(2.1.1) KOD-PCNA and Pfu-PCNA
PCNA-related sites for multimer formation are PCNA derived from Thermococcus kodakaraensis (hereinafter also referred to as “KOD-PCNA”) (SEQ ID NO: 14), Pyrococcus furiosus PCNA (hereinafter “Pfu-PCNA”). (SEQ ID NO: 13) includes an N-terminal region consisting of amino acids 82, 84 and 109 and a C-terminal region consisting of amino acids 139, 143 and 147. The N-terminal region is positively charged, the C-terminal region is negatively charged, and multimers are formed by interaction.

The description given by taking SEQ ID NO: 13 or SEQ ID NO: 14 as an example also applies to PCNA other than the PCNA whose sequence is specifically presented herein. For example, as shown in FIG. 4, in the PCNA other than the PCNA shown in SEQ ID NOs: 13 and 14, a region related to multimer formation consisting of amino acids 82, 84, 109, 139, 143, and 147 of SEQ ID NO: 13 Indicates the corresponding area. Here, when there are two different amino acid sequences, the amino acid or region “corresponds” in one of the reference amino acid sequences means that when the primary structure of the amino acid sequences is compared (aligned), The position corresponds to the position.

PCNA variants that load DNA alone are more preferably involved in PCNA multimer formation,
(A) N-terminal region consisting of amino acids corresponding to positions 82, 84 and 109, or (b) C-terminal region consisting of amino acids corresponding to positions 139, 143 and 147, having at least one modification and no RFC Both include mutants that are loaded into DNA and promote the elongation reaction by DNA polymerase.

For example, the amino acid corresponding to position 143 of SEQ ID NO: 13 is changed to a basic amino acid, the positions 82 and 143 are both changed to neutral amino acids, the position 147 is changed to a neutral amino acid, or 109 And the like, in which both the 145th and 143rd are modified to neutral amino acids. Examples of the neutral amino acid of the present invention include glycine, alanine, valine, leucine, isoleucine, phenylalanine, tyrosine, proline, serine, threonine, cysteine, methionine, asparagine, and glutamine as long as they are natural. Preferably, the alanine has the smallest influence on the three-dimensional structure of the peripheral site of the substitution site. Examples of basic amino acids include arginine, histidine, lysine, and tryptophan as long as they are natural. Arginine or lysine is preferable.

More preferably, in addition to the PCNA variant described in Patent Document 1, a sequence in which the 147th amino acid residue is substituted with alanine (D147A), the 82nd and 143rd amino acid residues are alanine. Sequence (R82A / D143A or R82A / E143A), and sequences in which the 109th and 143rd amino acid residues are substituted with alanine (R109A / D143A or R109A / E143A). It is not limited to.

Further, the PCNA used in the nucleic acid amplification reagent of the present invention may be a modified methionine corresponding to the 73rd position of SEQ ID NO: 13 or SEQ ID NO: 14 in order to increase the expression level. More preferable examples include those modified to M73L, but are not limited thereto.

(2.1.2) Mja-PCNA
Moreover, it is preferable that PCNA used for the nucleic acid amplification reagent of this invention is a PCNA monomer shown in either of the following (1) to (3).
[1] A polypeptide comprising an amino acid sequence in which the 142nd amino acid residue of the amino acid sequence of SEQ ID NO: 19 is substituted with a basic amino acid residue.
[2] In the PCNA monomer represented by [1], one or several amino acid residues other than the amino acid residue corresponding to position 142 in the amino acid sequence shown in SEQ ID NO: 19 are substituted or missing. A polypeptide comprising an amino acid sequence that has been deleted, inserted and / or added (collectively referred to as “mutation”) and having DNA polymerase amplification enhancing activity.
[3] A polypeptide comprising an amino acid sequence having 80% or more identity with the amino acid sequence represented by SEQ ID NO: 19, and having DNA polymerase amplification enhancing activity.

SEQ ID NO: 19 is the amino acid sequence of PCNA derived from Methanocaldococcus jannaschii (hereinafter also simply referred to as Mja). This amino acid sequence has been elucidated in Non-Patent Document 1, etc.

In SEQ ID NO: 19, the 142nd amino acid residue is one of the amino acid residues involved in PCNA multimer formation. Amino acid residues involved in PCNA multimer formation are present in the N-terminal region and C-terminal region of each monomer. The PCNA multimer is formed by joining the N-terminal region of one monomer and the C-terminal region of the other monomer as an interface. In eukaryotic cells and archaea, PCNA often forms trimers. In the amino acid sequence represented by SEQ ID NO: 19, the N-terminal region corresponds to the position of the group indicated by (a) below, and the C-terminal region corresponds to the position of the group indicated by (b) below.
(A) 80, 82, 108th amino acid residue group (b) 138, 142, 146th amino acid residue group

In the polypeptide of (2) above, one or several amino acid residues are substituted, deleted, inserted and / or added in the amino acid sequence shown in SEQ ID NO: 19 as long as the DNA polymerase amplification enhancing activity is retained. (Hereinafter, these are collectively referred to as “mutation”.) A polypeptide comprising an amino acid sequence. One or several mutations include restriction enzyme treatment, treatment with exonuclease, DNA ligase, etc., site-directed mutagenesis or random mutagenesis (Molecular Cloning, Third Edition, Chapter 13, Cold Spring Harbor Laboratory Press, New (York) and the like can be carried out by introducing mutation into DNA encoding the PCNA monomer of the present invention described later. The variant PCNA monomer can also be obtained by other methods such as ultraviolet irradiation. Variant PCNA monomers also include naturally occurring variants (for example, single nucleotide polymorphisms) such as those based on individual differences in microorganisms holding PCNA, differences in species or genera.

The polypeptide of [3] above is a polypeptide having an amino acid sequence that retains DNA polymerase amplification enhancing activity and has an identity of 80% or more compared to the amino acid sequence shown in SEQ ID NO: 19. is there. Preferably, the identity between the amino acid sequence of the PCNA monomer of the present invention and the amino acid sequence shown in SEQ ID NO: 19 is 85% or more, more preferably 88% or more, still more preferably 90% or more, and even more. Preferably it is 93% or more, more preferably 95% or more, particularly preferably 98% or more, and most preferably 99% or more. Such a polypeptide comprising an amino acid sequence having a certain identity or more can be prepared based on the known genetic engineering techniques as described above.

As PCNA as described in [2] or [3] above, more preferably, those having an affinity tag such as a His tag inserted at the N-terminus for easy purification of PCNA can be mentioned. There is no particular limitation.

In the PCNA monomer, the 142nd amino acid residue in SEQ ID NO: 19 is substituted with a basic amino acid residue, but the type of basic amino acid to be substituted is not particularly limited. Examples of basic amino acids include arginine, histidine, lysine, and tryptophan as long as they are natural. Arginine or lysine is preferable.

(2.2)
The above-mentioned method for obtaining PCNA involves transferring the PCNA gene to an expression vector as necessary, transforming, for example, Escherichia coli as a host using the expression vector, and then applying it to an agar medium containing a drug such as ampicillin. To form. The colony is inoculated in a nutrient medium such as LB medium or 2 × YT medium and cultured at 37 ° C. for 12 to 20 hours, and then the cells are crushed and the crude enzyme solution is extracted. A vector derived from pBluescript is preferable. Any known method may be used as a method for crushing bacterial cells. For example, ultrasonic treatment, a physical crushing method such as French press or glass bead crushing, or a lytic enzyme such as lysozyme can be used. . This crude enzyme solution is heat-treated at 80 ° C. for 30 minutes and centrifuged to remove the host-derived protein and subjected to SDS-PAGE to confirm the expression of the target protein.

Any method may be used as a method for obtaining purified PCNA from the strain selected by the above method, for example, the following method. After the cells obtained by culturing in the nutrient medium are collected, the crude enzyme solution is obtained by crushing and extracting by an enzymatic or physical crushing method. The obtained crude enzyme extract is heat-treated, for example, at 80 ° C. for 30 minutes, and then the PCNA fraction is recovered by ammonium sulfate precipitation. This crude enzyme solution can be desalted by a method such as gel filtration using Sephadex G-25 (manufactured by Amersham Pharmacia Biotech). After this operation, it can be separated and purified by Q Sepharose column chromatography to obtain a purified enzyme preparation. The purified enzyme preparation is purified by SDS-PAGE to such an extent that it shows almost a single band.

(2.3) DNA polymerase amplification enhancing activity Whether the PCNA mutant can be loaded into DNA alone (having DNA polymerase amplification enhancing activity) can be evaluated by PCR. PCNA to be evaluated is added to a PCR reaction solution containing DNA as a template, buffer material, magnesium, dNTPs, primers, and DNA polymerase belonging to Family B, with or without wild-type PCNA added, and DNA By comparing the amount of amplification, it can be confirmed whether or not the DNA can be loaded alone. Even if wild-type PCNA or other PCNA that cannot be loaded into DNA alone is added, the amount of DNA amplified by PCR does not change, but rather the amount of DNA amplified tends to be reduced. On the other hand, a mutant that can be loaded into DNA alone can be evaluated for DNA polymerase amplification enhancing activity by comparing with a mutant without addition of PCNA.

In the present invention, the evaluation of “whether the PCNA mutant can be loaded on DNA alone” (evaluation of DNA polymerase amplification enhancing activity) is according to the following method.
Using 10 × PCR Buffer (concentrated to 10 times the concentration used in the reaction) attached to KOD Dash (manufactured by Toyobo)
1 × PCR Buffer,
0.2 mM dNTPs,
15 pmol of the primers according to SEQ ID NOS: 15 and 16, which amplify DNA of about 3.6 kb,
10 ng of human genomic DNA (Roche's Human Genomic DNA; model number 116111112001),
Prepare a reaction solution containing 1U KOD-Plus-DNA polymerase,
250 ng of PCNA to be evaluated is added to 50 μl of the reaction solution, and PCR is performed on a schedule of repeating 30 cycles of 98 ° C., 10 seconds → 68 ° C., 30 seconds after the pre-reaction at 94 ° C. for 30 seconds. After completion of the reaction, 1% agarose electrophoresis is performed on 5 μl of the reaction solution, ethidium bromide staining is performed, and the amplified DNA fragment of about 3.6 kb under ultraviolet irradiation is compared with the one added with wild type PCNA alone. It can be evaluated whether it can be loaded into PCNA. PCNA that can be loaded into DNA alone increases the amount of amplified DNA.

In the present invention, as a method for quantitatively evaluating the increase in the amount of amplified DNA, the amount of amplified DNA is digitized by using Gel Pro Analyzer (Media Cybernetics), which is an electrophoresis pattern analysis software. . When comparing the DNA amplification amount by such a method, the DNA amplification amount when PCNA is added is 1.0 times (preferably 1.2 times, more preferably when DNA amplification is not added). Exceeds 1.5 times, more preferably 2 times and 3 times. Alternatively, if the target DNA that has not been amplified is amplified, it is determined that the PCNA has “DNA polymerase amplification enhancing activity”.

The modification of PCNA can be performed in the same manner as the modification of DNA polymerase.

In the nucleic acid amplification reagent of the present invention described above, the DNA synthesis substrate is typically composed of four types of deoxynucleotide triphosphates, dATP, dCTP, dGTP, and dTTP, except for dATP, dCTP, dGTP, and dTTP. It may also contain a deoxynucleotide triphosphate such as dUTP or dITP.

The primer used in the above-described nucleic acid amplification reagent of the present invention is typically composed of nucleotides consisting of 4 bases of adenine, cytosine, guanine and thymine. In the nucleic acid amplification reagent of the present invention, adenine, cytosine and guanine are used. And nucleotides other than thymine, such as uracil and inosine.

Hereinafter, the present invention will be specifically described by way of examples. The description of the following examples does not specifically limit the present invention.

(Example 1-1)
Production of KOD DNA polymerase mutants Modified thermostable DNA polymerases derived from Thermococcus kodakaraensis KOD1 strain (Y7A / V93K / H147E and Y7A / P36H / N210D mutation) for use in the examples described below. A) A plasmid containing the gene was prepared. As a DNA template used for mutagenesis, a modified heat-resistant DNA polymerase gene (SEQ ID NO: 17) (pKOD) derived from Thermococcus kodakaraensis KOD1 strain cloned in pBluescript was used. Mutation was introduced using a KOD-Plus-Mutageness Kit (Toyobo) according to the instruction manual. The mutant was confirmed by decoding the base sequence. Escherichia coli JM109 was transformed with the obtained plasmid and used for enzyme preparation.
(Example 1-2)
Preparation of Pfu DNA polymerase mutant A plasmid containing a modified thermostable DNA polymerase (Y7A / P36H / N210D mutant) gene derived from Pyrococcus furiosus strain was prepared for use in the examples described later. As a DNA template used for mutagenesis, a modified thermostable DNA polymerase gene (SEQ ID NO: 35) (pPfu) derived from Pyrococcus furiosus cloned in pBluescript was used. Mutation was introduced using a KOD-Plus-Mutageness Kit (Toyobo) according to the instruction manual. The mutant was confirmed by decoding the base sequence. Escherichia coli JM109 was transformed with the obtained plasmid and used for enzyme preparation.

(Example 2)
Production of modified thermostable DNA polymerase The cells obtained in Example 1 were cultured as follows. First, 80 mL of TB medium (Molecular cloning 2nd edition, p.A.2) containing sterilized 100 μg / mL ampicillin was dispensed into a 500 mL Sakaguchi flask. Escherichia cultivated at 37 ° C. for 16 hours in 3 mL of LB medium (1% bactotryptone, 0.5% yeast extract, 0.5% sodium chloride; Gibco) containing 100 μg / mL ampicillin in advance in this medium. Coli JM109 (plasmid transformant) (using a test tube) was inoculated and cultured at 37 ° C. for 16 hours with aeration. The cells are collected from the culture solution by centrifugation, suspended in 50 mL of disruption buffer (30 mM Tris-HCl buffer (pH 8.0), 30 mM NaCl, 0.1 mM EDTA), and then subjected to sonication. By crushing, a cell lysate was obtained. Next, the cell lysate was treated at 80 ° C. for 15 minutes, and then the insoluble fraction was removed by centrifugation. Furthermore, nucleic acid treatment using polyethyleneimine, ammonium sulfate precipitation, and heparin sepharose chromatography were performed. Finally, storage buffer (50 mM Tris-HCl buffer (pH 8.0), 50 mM potassium chloride, 1 mM dithiothreitol, 0 1% Tween 20, 0.1% Nonidet P40, 50% glycerin) to obtain a modified thermostable DNA polymerase. The DNA polymerase activity in the purification step was measured according to the above DNA polymerase activity measurement method. When the enzyme activity was high, the sample was diluted for measurement.

(Example 3)
Preparation of KOD-PCNA1 mutant A plasmid containing a modified thermostable PCNA1 (M73L / D147A mutant) gene derived from Thermococcus kodakaraensis KOD1 strain was prepared. As a DNA template used for mutagenesis, PCNA (SEQ ID NO: 18) (pKODPCNA) derived from Thermococcus kodakaraensis KOD1 strain cloned in pBlueScript was used. Mutation was introduced using a KOD-Plus-Mutageness Kit (manufactured by Toyobo) according to the instruction manual. The mutant was confirmed by decoding the base sequence. Escherichia coli DH5α was transformed with the obtained plasmid and used for enzyme preparation.

Example 4
Production of KOD-PCNA1 The cells obtained in Example 3 were cultured as follows. First, 80 mL of TB medium (Molecular cloning 2nd edition, p.A.2) containing sterilized 100 μg / mL ampicillin was dispensed into a 500 mL Sakaguchi flask. Escherichia cultivated at 37 ° C. for 16 hours in 3 mL of LB medium (1% bactotryptone, 0.5% yeast extract, 0.5% sodium chloride; Gibco) containing 100 μg / mL ampicillin in advance in this medium. E. coli DH5α (plasmid transformant) (using a test tube) was inoculated and cultured at 37 ° C. for 16 hours with aeration. The cells are collected from the culture solution by centrifugation, suspended in 50 mL of disruption buffer (30 mM Tris-HCl buffer (pH 8.0), 30 mM NaCl, 0.1 mM EDTA), and then subjected to sonication. By crushing, a cell lysate was obtained. Next, the cell lysate was treated at 80 ° C. for 15 minutes, and then the insoluble fraction was removed by centrifugation. Furthermore, nucleic acid treatment using polyethyleneimine, ammonium sulfate salting out, and Q sepharose chromatography were performed. Finally, a storage buffer (50 mM Tris-HCl buffer (pH 8.0), 50 mM potassium chloride, 1 mM dithiothreitol, 0 1% Tween20, 0.1% Nonidet P40, 50% glycerin) to obtain modified heat-resistant PCNA.

(Example 5)
Plasmid preparation of Mja-PCNA mutant A plasmid containing a modified heat-resistant PCNA gene mutant (E142K) derived from Methanocaldococcus jannaschii strain was prepared. As a DNA template used for mutagenesis, PCNA (SEQ ID NO: 34) (pMjaPCNA) derived from Methanocaldococcus jannaschii strain cloned in pET23b was used. Mutation was introduced using a KOD-Plus-Mutageness Kit (manufactured by Toyobo) according to the instruction manual. The mutant was confirmed by decoding the base sequence. Escherichia coli BL21 (DE3) pLysS was transformed with the obtained plasmid and used for enzyme preparation.

(Example 6)
Production of Mja-PCNA The cells obtained in Example 1 were cultured as follows. First, 80 mL of LB medium (1% bactotryptone, 0.5% yeast extract, 0.5% sodium chloride; manufactured by Gibco) containing 100 μg / mL ampicillin that was sterilized was dispensed into a 500 mL Sakaguchi flask. This medium was inoculated with Escherichia coli BL21 (DE3) pLysS (plasmid transformant) (using a test tube) previously cultured at 37 ° C. for 16 hours in 3 mL LB medium containing 100 μg / mL ampicillin at 37 ° C. Then, aeration culture was performed until OD600 became 0.3 to 0.6. Thereafter, IPTG was added to a final concentration of 0.5 mM, and aeration culture was performed for 4 hours. The cells are collected from the culture solution by centrifugation, suspended in 50 mL of disruption buffer (30 mM Tris-HCl buffer (pH 8.0), 30 mM NaCl, 0.1 mM EDTA), and then subjected to sonication. By crushing, a cell lysate was obtained. Next, the cell lysate was treated at 80 ° C. for 15 minutes, and then the insoluble fraction was removed by centrifugation. Furthermore, nucleic acid treatment using polyethyleneimine, ammonium sulfate salting out, and Q sepharose chromatography were performed. Finally, a storage buffer (50 mM Tris-HCl buffer (pH 8.0), 50 mM potassium chloride, 1 mM dithiothreitol, 0 1% Tween20, 0.1% nonidet P40, 50% glycerin) to obtain an Mja-PCNA mutant.

(Example 7)
Amplification of long target DNA KOD DNA polymerase mutant (Y7A / V93K / H147E), KOD-PCNA1 M73L / D147A mutant is used to amplify 17.5 kb of DNA with and without PCNA. Comparison of DNA amplification was performed. In each of the above cases, DNA amplification was compared with and without betaine. For PCR, KOD-Plus-Ver. 2 (manufactured by Toyobo Co., Ltd.)
1 × PCR Buffer,
1.5 mM MgSO ₄ ,
0.2 mM dNTPs,
15 pmol of the primers according to SEQ ID NOs: 20 and 21, which amplify DNA of about 8.5 kb,
300, 30, and 3 copies of human genomic DNA (Roche Human Genomic DNA; model number 116111112001), and
500 ng of KOD-PCNA1 mutant (M73L / D147A) was added (or not added) to 50 μl of a reaction solution containing 1.25 U KOD DNA polymerase mutant (Y7A / V93K / H147E) mixed with 1 μg of KOD antibody. In addition, the reaction systems were compared by adding (or not adding) 1M betaine.

As a control, one without PCNA was also carried out. PCR system GeneAmp (registered trademark) 9700 (Applied Biosystem, Inc.) with a cycle of 40 cycles of 94 ° C, 2 minutes before reaction, 98 ° C, 10 seconds → 65 ° C, 10 seconds → 68 ° C, 4 minutes 30 seconds ) Was used to perform PCR. After completion of the reaction, 1% agarose electrophoresis was performed on 5 μl of the reaction solution, ethidium bromide staining was performed, and the amplification amount of the amplified DNA fragment was confirmed under ultraviolet irradiation.

FIG. 1 shows a comparison of amplification by amplifying about 8.5 kb of DNA from a low-copy template with and without KOD-PCNA1 mutant and with and without betaine in each of the above cases. It will be.

As a result, no DNA amplification could be confirmed without PCNA and betaine. In addition, with PCNA and without betaine, although DNA amplification could be confirmed, the specificity was poor, and lanes in which DNA amplification was not observed were observed. When PCNA was not present and betaine was present, DNA amplification was confirmed, but amplification efficiency was poor, and amplification from three copies resulted in a small amount of DNA amplification. On the other hand, with PCNA and betaine, specificity was high, and sufficient DNA amplification was confirmed even from a low copy such as 3 copies. Long target DNA has a long extension time and is likely to cause non-specific amplification. Although PCNA is excellent in the function of increasing the amplification efficiency, DNA is amplified from a misannealed primer, resulting in poor reaction specificity. Betaine, on the other hand, not only increases amplification efficiency, but also improves reaction specificity. By combining these, it is considered that excellent amplification efficiency can be obtained while improving reaction specificity. It is done.

(Example 8)
Amplification of target DNA having a region with high GC ratio KOD DNA polymerase mutant (Y7A / V93K / H147E), KOD-PCNA1 M73L / D147A mutant, 5 types of systems for amplifying DNA of about 10 kb (these 5 types are A region of 500 bp or more in which the GC rate exceeds 70% is included inside.), And DNA amplification was compared with and without PCNA. In each of the above cases, DNA amplification was compared with and without betaine. For PCR, KOD-Plus-Ver. 2 (manufactured by Toyobo Co., Ltd.)
1 × PCR Buffer,
1.5 mM MgSO ₄ ,
0.2 mM dNTPs,
6 pmol primers for amplifying about 10 kb (ATCB: SEQ ID NO: 22 and 23, BRAF: SEQ ID NO: 24 and 25, TGFb: SEQ ID NO: 26 and 27, ACE: SEQ ID NO: 28 and 29, CASP3: SEQ ID NO: 30 and 31),
20 ng of human genomic DNA (Roche Human Genomic DNA; model number 116111112001), and
0.6U KOD DNA polymerase mutant (Y7A / V93K / H147E) mixed with 0.5 μg KOD antibody
The reaction system was compared by adding (or not adding) betaine to 20 μl of the reaction solution containing 1 mg of PCNA mutant (or not adding it). As a control, PCNA and betaine were not added. The cycle is 94 ° C., 2 minutes before the reaction, and then PCR system GeneAmp (registered trademark) 9700 (Applied Biosystem) is used in a schedule that repeats 30 cycles of 98 ° C., 10 seconds → 60 ° C., 10 seconds → 68 ° C., 2 minutes. PCR was performed.

FIG. 2 shows the results of electrophoresis of the products obtained by performing PCR with and without KOD-PCNA1 mutant, and with and without betaine in each of the above cases.

As a result, when neither betaine nor PCNA existed, DNA amplification was not observed in all five species. When betaine was not added and KOD-PCNA1 mutant was added, only CASP3 in lane 5 was able to confirm DNA amplification, but smear occurred and the amplification product band could not be confirmed. The success rate was low. In the case where betaine was added and PCNA was not added, it was confirmed that there was a thin band in ATCB in lane 1 and CASP3 in lane 5, but the amplification efficiency was poor. On the other hand, in the case where both betaine and PCNA were added, DNA amplification could be confirmed in all five types although the ACE band in lane 4 was thin. The region containing GC is difficult to amplify and requires excellent amplification efficiency. This target DNA is also as long as 10 kb, and the reaction specificity is important. Combining PCNA and betaine enabled efficient DNA amplification while maintaining excellent reaction specificity.

Example 9
Two types of KOD DNA polymerase mutant (Y7A / P36H / N210D) and Pfu polymerase mutant (Y7A / P36H / N210D) as DNA amplified DNA polymerase from plant lysate , KOD-PCNA1 mutant (M73L / D147A) as PCNA, Using two types of Mja-PCNA mutants (E142K), whether or not PCR can be performed without purification from plant lysate was compared with and without betaine. As a template, a tobacco leaf 3 mm square was added to 100 μl of Buffer A (100 mM Tris-HCl (pH 9.5), 1M KCl, 10 mM EDTA) and heat-treated at 95 ° C. for 10 minutes, and used as a lysate. For PCR, a 10 × PCR Buffer attached to KOD Dash (Toyobo) was used.
1 × PCR Buffer,
0.2 mM dNTPs,
15 pmol of the primers according to SEQ ID NOs: 32 and 33, which amplify about 1.3 kb,
1000 ng of PCNA to be evaluated was added (or not added) to 50 μl of a reaction solution containing a 1.25 U DNA polymerase mutant (KOD, Pfu each Y7A / P36H / N210D mutant) mixed with 1 μg of KOD antibody, Moreover, the betaine compared the thing which does not contain what contains 1M. As a control, PCNA and betaine were not added. PCR system GeneAmp (registered trademark) 9700 (Applied Biosystem) with a schedule of cycles of 94 ° C, 2 minutes pre-reaction, and 35 cycles of 98 ° C, 10 seconds → 65 ° C, 10 seconds → 68 ° C, 1.5 minutes PCR was performed using
After completion of the reaction, 1% agarose electrophoresis was performed on 5 μl of the reaction solution, ethidium bromide staining was performed, and the amplification amount of the amplified DNA fragment was confirmed under ultraviolet irradiation.

FIG. 3 shows the plant lysate by adding 1000 ng of KOD-PCNA1 mutant or Mja-PCNA mutant with and without betaine of KOD DNA polymerase mutant (Y7A / P36H / N210D). The results of electrophoresis after electrophoresis without purification were shown. For comparison, a sample without PCNA added was also carried out.

Plant lysates contain a large amount of PCR-inhibiting substances, and are known to cause inhibition when subjected to PCR. In the case where neither betaine nor PCNA was added, inhibition occurred when 2 μl of lysate was added to 50 μl of reactivity. Inhibition occurred at 4 μl when betaine was not added and the Mja-PCNA mutant was used, and inhibition occurred at 8 μl when betaine was not added and KOD-PCNA1 mutant was used. In each of the cases described above, addition of betaine to each of them prevented inhibition even when doubled lysate was added. It was confirmed that the combination of betaine and PCNA strengthened inhibition. It was found that betaine and PCNA have independent functions, and an excellent amplification performance can be obtained by combining these functions.

The same result was obtained with the Pfu DNA polymerase mutant (Y7A / P36H / N210D). In the case where neither betaine nor PCNA was added, inhibition occurred when 2 μl of lysate was added to 50 μl of reactivity. Inhibition occurred at 4 μl when betaine was not added and the Mja-PCNA mutant was used, and inhibition occurred at 8 μl when betaine was not added and KOD-PCNA1 mutant was used. In each of the cases described above, addition of betaine to each of them prevented inhibition even when doubled lysate was added. It turned out that the kind of polymerase is not ask | required for the combination of betaine and PCNA.

The present invention is useful in biotechnology-related industries, and is particularly useful in technologies relating to DNA synthesis regardless of research use or diagnostic use.

Claims (7)

A nucleic acid amplification reagent comprising DNA polymerase belonging to family B, Proliferating Cell Nuclear Antigen (PCNA), and betaine, wherein the PCNA consists of any of the following (1) or (2) Nucleic acid amplification reagent characterized.
(1) A polypeptide comprising an amino acid sequence in which one to several amino acid residues are substituted, deleted, inserted or added in the amino acid sequence shown in SEQ ID NO: 13, and having DNA polymerase amplification enhancing activity ( 2) A polypeptide comprising an amino acid sequence having a homology with the amino acid sequence of SEQ ID NO: 13 of 80% or more and having DNA polymerase amplification enhancing activity A nucleic acid amplification reagent comprising a DNA polymerase belonging to family B, PCNA and betaine, wherein the PCNA consists of any of the following (1) or (2):
(1) A polypeptide comprising an amino acid sequence in which one to several amino acid residues are substituted, deleted, inserted or added in the amino acid sequence shown in SEQ ID NO: 14 and having DNA polymerase amplification enhancing activity ( 2) A polypeptide comprising an amino acid sequence having a homology with the amino acid sequence of SEQ ID NO: 14 of 80% or more and having DNA polymerase amplification enhancing activity A nucleic acid amplification reagent comprising a DNA polymerase belonging to family B, PCNA and betaine, wherein the PCNA consists of any of the following (1) or (2):
(1) A polypeptide comprising an amino acid sequence in which one to several amino acid residues are substituted, deleted, inserted or added in the amino acid sequence shown in SEQ ID NO: 19, and having a DNA polymerase amplification enhancing activity ( 2) A polypeptide comprising an amino acid sequence having a homology with the amino acid sequence of SEQ ID NO: 19 of 80% or more and having DNA polymerase amplification enhancing activity The nucleic acid amplification reagent according to any one of claims 1 to 3, wherein the DNA polymerase belonging to Family B is an archaea-derived DNA polymerase. The nucleic acid amplification reagent according to any one of claims 1 to 4, wherein the DNA polymerase belonging to family B is an archaeal DNA polymerase mutant having reduced base analog detection activity. The nucleic acid amplification reagent according to any one of claims 1 to 5, wherein the DNA polymerase belonging to Family B has at least one amino acid modification in any of the amino acids constituting the 3'-5 'exonuclease active region. . The nucleic acid amplification reagent according to any one of claims 1 to 6, wherein the PCNA is a mutant PCNA having amplification enhancing activity.