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 exponential ly growing bacteria and in mutY and mutM mutants, which accumulate mismatch es between 8-oxoguanine (8-oxoG) and adenine residues in DNA. Conversely, G C --> 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 Mut S-dependent repair can correct 8-oxoG:A mismatches in Escherichia coli cell s but may not be able to compete with mutation fixation by MutY in mutT mut ants.