Reduction of GC → TA Transversion Mutation by Overexpression of MutS in Escherichia coli K-12

Overexpression of the MutS repair protein significantly decreased the rate of lacZ GC → TA transversion mutation in stationary-phase and exponentially growing bacteria and in mutY and mutM mutants, which accumulate mismatches between 8-oxoguanine (8-oxoG) and adenine residues in DNA. Conversely, GC → TA transversion increased in mutL or mutS mutants in stationary phase. In contrast, overexpression of MutS did not appreciably reduce lacZ AT → CG transversion mutation in a mutT mutant. These results suggest that MutS-dependent repair can correct 8-oxoG:A mismatches in Escherichia coli cells but may not be able to compete with mutation fixation by MutY in mutT mutants.