MMS mutagenesis in strains of Escherichia coli carrying the R46 mutagenic enhancing plasmid: phenotypic analysis of Arg+ revertants.

Arg+ revertants of E. coli AB1157 and derivative strains were selected after MMS mutagenesis and subjected to a phenotypic analysis which permitted the partitioning of revertants into 4 classes. The distribution of these revertant classes was influenced by mutations affecting DNA-repair systems, mutagen treatment and revertant-selection methods. Introduction of the R46 plasmid into strains also affected this mutational specificity, and it was concluded that the plasmid's mutagenic enhancing effect does not merely augment the cellular error-prone capacity to repair MMS damage to DNA.