Role of the 5' --> 3' exonuclease and Klenow fragment of Escherichia coli DNA polymerase I in base mismatch repair.
We have previously demonstrated that the Escherichia coli strain mutS DeltapolA had a higher rate of transition and minus frameshift mutations than mutS or DeltapolA strains. We argued that DNA polymerase I (PolI) corrects transition mismatches. PolI, encoded by the polA gene, possesses Klenow and 5' --> 3' exonuclease domains. 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. The Klenow-defective or 5' --> 3' exonuclease-defective mutS strains showed a marked increase in transition mutations. Sites of transition mutations in mutS, Klenow-defective mutS and 5' --> 3' exonuclease-defective mutS strains are different. 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. Transition hot and warm spots in mutS+ polA+ strains were found to differ from those in mutS and mutS DeltapolA strains. 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.
Imai
Masaru
M
Graduate School of Life Sciences, Tohoku University, Sendai, 980-8577, Japan.
Tago
Yu-ichiro
Y
Ihara
Makoto
M
Kawata
Masakado
M
Yamamoto
Kazuo
K
D053843:DNA Mismatch Repair; D004256:DNA Polymerase I / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics*; D005092:Exonucleases / Q000737:chemistry / Q000378:metabolism*; D051719:MutS DNA Mismatch-Binding Protein / Q000737:chemistry / Q000378:metabolism*; D009154:Mutation / Q000235:genetics
D004256:DNA Polymerase I; D005092:Exonucleases; D051719:MutS DNA Mismatch-Binding Protein