Mutat Res 254:27–35Īkasaka S, Yamamoto K (1994) Hydrogen peroxide induces G:C to T:A and G:C to C:G transversions in the supF gene of Escherichia coli. Biochem Biophys Res Commun 261:584–589Īkasaka S, Yamamoto K (1991) Construction of Escherichia coli K12 phr deletion and insertion mutants by gene replacement. We thus argue that all the spontaneous transition mutations in the wild-type strain do not arise from transition mismatches left unrepaired by the MutS system or MutS PolI system.Īgemizu Y, Uematsu N, Yamamoto K (1999) DNA sequence analysis of spontaneous tonB deletion mutations in a polA1 strain of Escherichia coli K12. Transition hot and warm spots in mutS + polA + strains were found to differ from those in mutS and mutS ΔpolA strains. Thus, it is suggested that, in addition to mutS function, both the Klenow and 5´ → 3´ exonuclease domains are involved in the decrease of transition mutations. Sites of transition mutations in mutS, Klenow-defective mutS and 5´ → 3´ exonuclease-defective mutS strains are different. The Klenow-defective or 5´ → 3´ exonuclease-defective mutS strains showed a marked increase in transition mutations. In the present study, rates of mutation were found to be higher in Klenow-defective mutS strains and 5´ → 3´ exonuclease-defective mutS strains than mutS or polA strains. PolI, encoded by the polA gene, possesses Klenow and 5´ → 3´ exonuclease domains. We argued that DNA polymerase I (PolI) corrects transition mismatches. We have previously demonstrated that the Escherichia coli strain mutS ΔpolA had a higher rate of transition and minus frameshift mutations than mutS or ΔpolA strains.
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