MUTY REPAIR IS MUTAGENIC IN MUTT(-) STRAINS OF ESCHERICHIA-COLI

We have determined the numbers and types of mutations that occur in st rains 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 th e 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.