Role of the 5' --> 3' exonuclease and Klenow fragment of Escherichia coli DNA polymerase I in base mismatch repair

Mol Genet Genomics. 2007 Aug;278(2):211-20. doi: 10.1007/s00438-007-0239-8. Epub 2007 Apr 25.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • DNA Mismatch Repair*
  • DNA Polymerase I / chemistry
  • DNA Polymerase I / metabolism*
  • Escherichia coli / enzymology*
  • Escherichia coli / genetics*
  • Exonucleases / chemistry
  • Exonucleases / metabolism*
  • MutS DNA Mismatch-Binding Protein / chemistry
  • MutS DNA Mismatch-Binding Protein / metabolism*
  • Mutation / genetics


  • DNA Polymerase I
  • Exonucleases
  • MutS DNA Mismatch-Binding Protein