Induction of UMUC+ gene expression in Escherichia coli irradiated by near ultraviolet light

The induction of umu+ gene expression caused by irradiation with near ultraviolet light (BLB; black light blue) was studied in Escherichia coli K-12 strains with special reference to the effects of SOS repair deficiencies. The umuC+ gene expression was measured as the enzymic activity of β-galactosidase which is regulated by the promoter of the umuC+ operon carried in a plasmid DNA carrying a promoter of umuC+ operon, a umuD+ gene and a umuC+-lacZ+ gene fusion. A high induction of the umuC+ gene expression was observed in the uvrA cells in the case of BLB or UV irradiation as compared with the parental wild-type cells. Caffeine inhibited the induction of the umuC+ gene expression due to BLB or UV irradiation in both strains. There was very little induction in lexA and recA mutants. In contrast with UV irradiation, there was no killing of cells by BLB irradiation in any strain (wild, uvrA, lexA and recA). Possible implications of the experimental results were discussed. (author)