MutY repair is mutagenic in mutT- strains of Escherichia coli.

We have determined the numbers and types of mutations that occur in strains of Escherichia coli defective in mutT and (or) mutY repair. High rates of C.G to A.T mutations in mutY- cells are unaffected by the status of mutT. However, mutT-/mutY+ strains have higher rates of A.T to C.G mutations than mutT-/mutY- strains. This result indicates that the high rates of A.T to C.G mutations seen in mutT- strains of E. coli are due in part to the activity of the mutY repair system. We conclude that mutY repair is mutagenic in a mutT- background.