Endonuclase-assisted isothermal amplification using contamination-free reagents
Disclosed are methods and kits for endonuclease-assisted DNA amplification reaction using decontaminated primer solutions that are pre-treated with a nuclease. Nucleic acid amplification assays that employ nuclease-resistant, inosine-containing primers, endonuclease V enzymes to introduce a nick into a target DNA comprising at least one inosine, and a DNA polymerase to generate amplicons of a target DNA are also disclosed.
1. A method of producing at least one amplicon based on a target DNA comprising:
(a) providing the target DNA;
(b) providing a primer solution comprising at least one exonuclease-resistant, inosine-containing primer, wherein said inosine-containing primer comprises at least one inosine residue or inosine analogue in its sequence;
(c) generating a DNA amplification reaction mixture by mixing together the target DNA, the primer solution, at least one 5′→3′ exonuclease-deficient DNA polymerase having a strand displacement activity, and at least one endonuclease that is capable of nicking an inosine-containing strand of a double stranded DNA at a residue 3′ to an inosine residue or inosine analogue; and
(d) incubating the DNA amplification reaction mixture to amplify at least one portion of the target DNA using the at least one exonuclease-resistant, inosine-containing primer to produce the at least one amplicon,
wherein the nuclease-resistant, inosine-containing primer comprises a phosphorothioate linkage at the 3′ side, or both the 3′ and 5′ side of and adjacent to the inosine residue or inosine analogue.
2. The method claim 1 , wherein the primer solution further comprises free deoxynucleotide triphosphates (dNTPs).
3. The method of claim 2 , wherein the primer solution further comprises DNA amplification buffer, formamide, single stranded DNA binding protein, ethylene glycol, Ficoll or combinations thereof.
4. The method of claim 1 further comprising decontaminating the primer solution, prior to generating the DNA amplification reaction mixture, by treating the primer solution with an exonuclease to remove any contaminating nucleic acids.
5. The method of claim 4 , further comprising inactivating the exonuclease in the primer solution after removal of any contaminating nucleic acids prior to generating the DNA amplification reaction mixture, and wherein optionally the target DNA is amplified under isothermal conditions.
6. The method of claim 1 , wherein the inosine residue or inosine analogue of the nuclease-resistant, inosine-containing primer is located at least 4 nucleotides downstream of the 5′ terminal nucleotide.
7. The method of claim 6 , wherein the inosine residue or inosine analogue of the nuclease-resistant, inosine-containing primer is located at the penultimate 3′ position.
8. The method of claim 1 , wherein the inosine-containing primer comprises at least 2 adjacent inosine residues or inosine analogues, wherein optionally the inosine residues are located both at the penultimate 3′ position and the 3′ terminal end of the inosine-containing primer.
9. The method of claim 1 , wherein:
i) the at least one 5′→3′ exonuclease-deficient DNA polymerase is selected from 5′→3′ exonuclease-deficient T7 DNA polymerase, 5′→3′ exonuclease-deficient Bst DNA polymerase, 5′→3′ exonuclease-deficient Klenow, 5′→3′ exonuclease-deficient delta Tts DNA polymerase, or combinations thereof;
ii) the primer solution comprises at least one inosine-containing forward primer and at least one inosine-containing reverse primer, wherein both the forward primer and the reverse primer are exonuclease-resistant; or
iii) the at least one nuclease-resistant, inosine-containing primer comprises an extender template.