| Near-Ultraviolet Mutagenesis in Superoxide Dismutase-deficient Strains of Escherichia coli Rick L. Knowles1 and Abraham Eisenstark2 1Division of Biological Sciences, University of Missouri,
Columbia, MO 65211 USA; 2Cancer Research Center, Columbia, MO
65201 USA Abstract
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. Futhermore, 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. Key words: A:T to T:A transversion, free radicals, hydroxyl radical, mutagenic specificity, near-UV radiation, superoxide anion, superoxide dismutase. Environ Health Perspect 102: 88-94(1994) Address correspondence to A. Eisenstark, Cancer Research Center, 3501 Berrywood Drive, Columbia, MO 65201 USA. We thank C. Cupples, D. Touati, and J. Imlay for kindly providing strains and for helpful discussion. This publication was made possible by grant number ES04889 from the National Institute of Environmental Health Sciences. Received 15 July 1993 ; accepted 20 October 1993.
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