Some Mismatch Repair Activities in Escherichia coli

Heterozygous bacteriophage λ DNA molecules, whose replication requires mismatch correction of a mutant nucleotide in the transcribed strand, provide an assay for localized mismatch repair in Escherichia coli. We describe two systems: one removes the A in C· A or G· A mismatches and the other removes one or the other C in a C· C mismatch. Mutations disabling the first system result in a mutator phenotype that may be identical to mutY.