Near-ultraviolet mutagenesis in superoxide dismutase-deficient strains of Escherichia coli.
We compared mutagenic spectra induced by polychromatic near-ultraviolet radiation (near-UV; 300-400 nm) with superoxide anion (O2-) -dependent mutagenesis using a set of Escherichia coli tester strains. Near-UV radiation produced increased frequencies of G:C to A:T transitions, G:C to T:A and A:T to T:A transversions, and small increases in frameshift mutations in wild-type cells. Tester strains lacking superoxide dismutase (SOD) activity (sodAsodB double mutants) demonstrated high spontaneous mutation frequencies and increased near-UV sensitivity. The double mutants also showed increased mutations induced by near-UV compared to either isogenic wild type, sodA or sodB single mutants. Furthermore, these mutants had an unusual spontaneous mutation spectrum, with a predominance of A:T to T:A transversions, followed by G:C to T:A transversions and frameshifts generated in runs of adenines in both the +1 and -1 direction. Other frameshifts were detected to a lesser degree. The oxygen dependency and the type of mutations spontaneously induced in SOD-deficient cells indicated that this mutagenic spectrum was caused by oxidative DNA damage. However, no apparent synergistic action between near-UV radiation and an increased flux of O2- could be detected. From the frequency and types of mutations induced by the two agents, we speculate that near-UV-induced mutagenesis and O2--dependent mutagenesis involve, in part, different lesion(s) and/or mechanism(s). The nature and possible mutagenic pathways of each are discussed.
Division of Biological Sciences, University of Missouri, Columbia, MO 65211 USA.
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D001426:Bacterial Proteins / Q000235:genetics*; D004249:DNA Damage; D004926:Escherichia coli / Q000235:genetics*; D009152:Mutagenicity Tests; D009154:Mutation; D010084:Oxidation-Reduction; D013482:Superoxide Dismutase / Q000235:genetics*; D013481:Superoxides / Q000378:metabolism; D014466:Ultraviolet Rays / Q000009:adverse effects*
D001426:Bacterial Proteins; D013481:Superoxides; C095500:SodA protein, Bacteria; C087504:SodB protein, Bacteria; D013482:Superoxide Dismutase