Mutations by near-ultraviolet radiation in Escherichia coli strains lacking superoxide dismutase.
In wild-type Escherichia coli, near-ultraviolet radiation (NUV) was only weakly mutagenic. However, in an allelic mutant strain (sodA sodB) that lacks both Mn- and Fe-superoxide dismutase (SOD) and assumed to have excess superoxide anion (O2-), NUV induced a 9-fold increase in mutation above the level that normally occurs in this double mutant. When a sodA sodB double mutant contained a plasmid carrying katG+ (excess HP-I catalase), mutation by NUV was reduced to wild-type (sodA+ sodB+) levels. Also, in the sodA sodB xthA triple mutant, which lacks exonuclease III (exoIII) in addition to SOD, the mutational frequency by NUV was reduced to wild-type levels. This synergistic action of NUV and O2- suggested that pre-mutational lesions occur, with exoIII converting these lesions to stable mutants. Exposure to H2O2 induced a 2.8-fold increase in mutations in sodA sodB double mutants, but was reduced to control levels when a plasmid carrying katG+ was introduced. These results suggest that NUV, in addition to its other effects on cells, increases mutations indirectly by increasing the flux of OH. radicals, possibly by generating excess H2O2.
Hoerter
J
J
Division of Biological Sciences, University of Missouri, Columbia 65211.
Eisenstark
A
A
Touati
D
D
D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000235:genetics* / Q000528:radiation effects; D006861:Hydrogen Peroxide / Q000378:metabolism; D009154:Mutation; D013482:Superoxide Dismutase / Q000502:physiology*; D013481:Superoxides / Q000378:metabolism*; D014466:Ultraviolet Rays
D013481:Superoxides; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase