Exonucleolytic proofreading by p53 protein

The tumour suppressor p53 protein plays an important role in maintaining genetic integrity. Recently, p53 was shown to have an intrinsic 3′→5′ exonuclease activity. The current study has extended the characterization of purified wild‐type recombinant p53‐associated 3′→5′ exonuclease function to demonstrate proofreading activity. p53‐associated 3′→5′ exonuclease shows clear preference for degradation of ssDNA over dsDNA substrate. On partial duplex structures, this exonucleolytic activity displays a marked preference for excision of a mismatched vs. a correctly paired 3′ terminus which enables the p53 protein to act as a proofreader. However, p53 displays variation in excision of mismatched base pairs. The results demonstrate that p53 exhibits mispair excision with a specificity of A:A > A:G > A:C opposite the template adenine residue and with a specificity of G:A > G:G > G:T opposite the template guanine residue. Hence, the observed specificity of mismatch excision shows that p53 exonucleolytic proofreading preferentially repairs transversion mutations. As part of an investigation of the functional interaction between p53 and DNA polymerase, the influence of p53 on the