Repair of defined single base-pair mismatches in Escherichia coli.

Heteroduplexes with single base-pair mismatches of known sequence were prepared by annealing separated strands of bacteriophage lambda DNA and used to transfect Escherichia coli. Each of the eight possible single base-pair mismatches was constructed. Genetic analysis of the progeny phages obtained from transfected bacteria indicates that the E. coli mismatch repair system does not recognize (or does not repair) all single base-pair mismatches with equal efficiency. In particular, the A.G, C.T, and C.C mismatches appear to be less repaired than any others. The mutator character of mismatch repair-deficient mutants suggests that such unrepaired mismatches should occur infrequently during E. coli DNA replication.