title: p53 enhances the fidelity of DNA synthesis by human immunodeficiency virus type 1 reverse transcriptase.
abstract: The tumor suppressor protein p53 plays a critical role in the maintenance of genetic integrity. p53 possesses 3'-->5' exonuclease activity, however, the significance of this function in DNA replication process remains elusive. It was suggested that 3'-->5' exonuclease activity of p53 may provide a proofreading function for DNA polymerases. In order to better understand the significance of this activity, the purified wild-type recombinant p53 was further evaluated for substrate specificity and for contribution to the accuracy of DNA synthesis. p53-associated 3'-->5' exonuclease displays 3' terminal nucleotide excision from RNA/DNA template-primer using ribosomal RNA as a template. The data demonstrate that p53 is highly efficient in removing a terminal mispair. Analysis of mispair excision opposite the template adenine residue shows that p53 catalyzes 3' terminal mismatch excision with a specificity of A : G>A : A>A : C. Hence, the observed specificity of mismatch excision indicates that p53 exonucleolytic proofreading preferentially repairs transversion mutations. The influence of the p53 on the accuracy of DNA synthesis was determined with exonuclease-deficient human immunodeficiency virus-1 (HIV-1) reverse transcriptase (RT), a key enzyme in the life cycle of the virus, that contributes significantly to the low accuracy of proviral DNA synthesis. Using an in vitro biochemical assay with recombinant purified HIV-1 RT, p53 and defined RNA/DNA or DNA/DNA template-primers, two basic features related to fidelity of DNA synthesis were studied: the misinsertion and mispair extension. The misincorporation of non-complementary deoxynucleotides into nascent DNA and subsequent mispair extension by HIV-1 RT were substantially decreased in the presence of p53 with both RNA/DNA and DNA/DNA template-primers. In addition, the productive interaction between polymerization (by HIV-1 RT) and exonuclease (by p53) activities was observed; p53 preferentially hydrolyzes mispaired 3'-termini, permitting subsequent extension of the correctly paired 3'-terminus by HIV-1 RT. Taken together the data demonstrate that preferential excision of mismatched nucleotides by 3'-->5' exonuclease activity of wild-type p53 enhances the fidelity of DNA synthesis by HIV-1 RT in vitro, thus providing a biochemical mechanism to reduce mutations caused by incorporation of mismatched nucleotides. The fact that p53 is reactive with both RNA/DNA and DNA/DNA template-primers raises an interesting possibility of the existence of functional cooperation between p53 and HIV-1 RT in cytoplasm during the reverse transcription process, which may be important for maintaining HIV genomic integrity.
authors.affiliation: Infectious Diseases Unit, Chaim Sheba Medical Center, Tel Hashomer 52621, Israel. bakhanus@yahoo.com
authors.forename: M
authors.initials: M
authors.lastname: Bakhanashvili
mesh_terms: D020137:Base Pair Mismatch; D004249:DNA Damage; D017931:DNA Primers; D004279:DNA, Viral / Q000096:biosynthesis*; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000378:metabolism* / Q000502:physiology; D054303:HIV Reverse Transcriptase / Q000378:metabolism* / Q000502:physiology; D015497:HIV-1 / Q000201:enzymology* / Q000235:genetics; D006801:Humans; D009692:Nucleic Acid Heteroduplexes; D012313:RNA; D013698:Templates, Genetic; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism* / Q000502:physiology
chemical_list: D017931:DNA Primers; D004279:DNA, Viral; D009692:Nucleic Acid Heteroduplexes; C034477:RNA primers; D016159:Tumor Suppressor Protein p53; D012313:RNA; D054303:HIV Reverse Transcriptase; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V