Mismatch-induced lethality due to a defect in Escherichia coli RecQ helicase in exonuclease-deficient background: Dependence on MutS and UvrD functions.

Escherichia coli DNA-unwinding protein RecQ has roles in the regulation of general recombination and the processing of stalled replication forks. In this study, we found that knockout of the recQ gene in combination with xonA xseA recJ mutations, which inhibit methyl-directed mismatch repair (MMR), caused about 100-fold increase in sensitivity to a purine analog 2-aminopurine (2AP). Intriguingly, inactivation of a MMR initiator due to the either mutation mutS or uvrD completely suppressed the 2AP sensitivity caused by recQ xonA xseA recJ mutations, suggesting that RecQ helicase might act on the DNA structures that are generated by the processing of DNA by the MutSLH complex and UvrD helicase. Moreover, the recQ gene knockout in combination with xonA xseA recJ mutations enhanced 2AP-induced filament formation, and increased by twofold the rate of spontaneous forward mutations in the thyA locus but did not increase the rate of rifampicin-resistant mutations. We discuss about the possible interplay between E. coli RecQ helicase and mismatch recognition factors.