Role of the supX gene in ultraviolet light-induced mutagenesis in Salmonella typhimurium.

Salmonella typhimurium strains with supX mutations are more sensitive than wild type to killing by ultraviolet (UV) irradiation. Studies with strains bearing the leuD21 mutation revealed that inactivation of the supX locus by a nonsense mutation or a deletion results in a complete lack of ability to produce induced Leu+ reversion mutations after UV irradiation. Suppression of the nonsense supX mutation or the presence of an Escherichia coli K-12 F'-borne supX+ allele restored the capacity for induced reversions and increased cell survival after UV irradiation. Introduction of plasmid pKM101 into supX mutant strains also restored their capacity for UV mutagenesis as well as increased survival. The possible nature of the supX gene product and mechanisms by which it may affect expression of the inducible SOS error-prone repair system are considered.