Mutagenic interaction between near-(365 nm) and far-(254 nm)ultraviolet radiation in repair-proficient and excision-deficient strains of Escherichia coli.
The mutational interaction between radiation at 365 and 254 nm was studied in various strains of E. coli by a mutant assay based on reversion to amino-acid independence in full nutrient conditions. In the two repair-proficient strains (K12 AB 1157 and B/r), pre-treatment with radiation at 365 nm strongly suppressed the induction of mutations by far-UV, a phenomenon accompanied by a strong lethal interaction. The frequency of mutations induced by far-UV progressively declined with increasing dose of near-UV. Far-UV-induced mutagenesis to T5 resistance was almost unaltered by pre-treatment with near-UV. In AB 1886 uvrA there was no lethal interaction between the two wavelengths but the mutagenic interaction was synergistic. This synergism was maximal at a 365-nm dose of 8 X 10(5) J m-2. It is proposed that in the wild-type strain, cells containing potentially mutagenic lesions are selectively eliminated from the population because of abortive excision of an error-prone repair-inducing signal. In excisionless strains, 365-nm radiation may be less damaging to the error-prone than to the error-free post-replication repair system. Alternatively, mutation may be enhanced because of the occurrence of error-prone repair of 365-nm lesions by a system that is not induced in the absence of 254-nm radiation.
D000596:Amino Acids / Q000378:metabolism; D003470:Culture Media; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000378:metabolism / Q000528:radiation effects*; D005787:Gene Frequency; D009154:Mutation; D013997:Time Factors; D014466:Ultraviolet Rays
D000596:Amino Acids; D003470:Culture Media