title: Characterization of Escherichia coli mutant strains deficient in AP DNA-repair synthesis.
abstract: Deficiency of apurinic/apyrimidinic (AP) DNA-repair enzymes in crude extracts of E. coli mutants was determined by following general and specific AP DNA-repair synthesis via nick translation in the presence of either all four dNTPs, or only one dNTP. We have shown that mutations either in DNA polymerase I or in AP endonucleases or in both, inhibit to different degrees the ability to repair AP DNA. The polA mutation totally abolishes the ability to perform both general and specific AP DNA repair, while the polAex mutation affects only general AP DNA repair. The xthA tight mutants, including the deletion mutant BW9101, can cope with small amounts of AP sites but hardly with high amounts of these lesions. In addition we have found that crude extracts of the xthA mutants degrade AP DNA by two modes: a nonspecific, and an AP-specific mode. These phenomena are common to all xth mutants and enabled us to discover this mutation. In contrast to the xth mutants so far isolated, BW2001 exhibits marked sensitivity to MMS and to X-ray irradiation. We found that this strain has a proficient DNA polymerase I but is absolutely deficient in AP endonucleases. We attribute its sensitivities to a secondary mutation at the structural gene of endonuclease IV.
mesh_terms: D001080:Apurinic Acid / Q000235:genetics*; D002474:Cell-Free System; D004256:DNA Polymerase I / Q000172:deficiency / Q000235:genetics; D004260:DNA Repair; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D043223:Deoxyribonuclease IV (Phage T4-Induced); D004706:Endodeoxyribonucleases / Q000172:deficiency / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D009154:Mutation; D011119:Polynucleotides / Q000235:genetics*
chemical_list: D029968:Escherichia coli Proteins; D011119:Polynucleotides; D001080:Apurinic Acid; D004256:DNA Polymerase I; D004706:Endodeoxyribonucleases; D043223:Deoxyribonuclease IV (Phage T4-Induced); C468972:endonuclease IV, E coli; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase