Interaction of an Escherichia coli mutator gene with a deoxyribonucleotide effector.

Strains of Escherichia coli carrying mutD5 display very high mutation rates (about 10(4)-fold above wild-type) when grown in rich medium, but relatively low mutation rates (about 10- to 50-fold above wild-type) in minimal medium. Thymidine, deoxycytidine, and deoxyuridine are all capable of stimulating mutation when added to minimal medium. Studies with mutants blocked in various steps of thymidine metabolism implicate a phosphorylated thymidine effector which mediates the mutagenic action of the added deoxyribonucleotides. In addition, an unidentified compound or compounds other than thymidine present in rich medium (L-broth) can also increase the mutation rate.