E.coli UNG was obtained from E.coli recombinant clones expressed by recombinant strains containing the E.coli UNG gene and refined by multi-step purification. It can effectively hydrolyze uracil on single- or double-stranded DNA, but is inactive against oligonucleotides less than 6 nt and inactive against RNA. E.coli UNG is not a heat-sensitive model and cannot be applied to reverse transcription