Provided are methods and compositions for activating oligonucleotide aptamer-deactivated DNA polymerases, comprising cleaving the aptamer by endonuclease V enzymatic activity to reduce or eliminate binding of the oligonucleotide aptamer to the DNA polymerase, thereby activating DNA synthesis activity of the DNA polymerase in a reaction mixture. Mixtures for use in methods of the invention are also provided. In some aspects, the oligonucleotide aptamer comprises one or more deoxyinosine nucleotides providing for aptamer-specific recognition and cleavage of the aptamer by the endonuclease V enzymatic activity. Exemplary oligonucleotide aptamers, mixtures and methods employing endonuclease V enzymatic activity are provided. The methods can be practiced using kits comprising a DNA polymerase-binding oligonucleotide aptamer and at least one endonuclease V enzymatic activity having oligonucleotide aptamer-specific recognition to provide for specific cleavage of the aptamer by the endonuclease V enzymatic activity.
