title: Killing of Escherichia coli K-12 by near-ultraviolet radiation in the presence of hydrogen peroxide: role of double-strand DNA breaks in absence of recombinational repair.
abstract: Near-ultraviolet (NUV) radiation killing of Escherichia coli K-12 can be enhanced by a sub-lethal concentration of hydrogen peroxide. This can be divided into a "RecA-dependent" and "RecA-independent" synergistic killing action. Stationary phase wild-type and 8 closely related repair-deficient mutants were examined for their NUV sensitivities in the presence and absence of H2O2. All exhibited the "RecA-independent" synergism; i.e., H2O2 enhanced NUV lethality when RecA repair was not operating. The "RecA-independent" synergism did not result from destruction of repair enzymes. Very few DNA--protein crosslinks could be detected following NUV plus H2O2 treatment. However, double-strand (DS) DNA breaks were produced, apparently by conversion of closely spaced single-strand (SS) breaks on opposite strands. The correlation between DS-break formation and lethality in wild-type and a polA mutant indicates that the RecA-independent synergistic killing results from the conversion of SS into lethal DS breaks.
mesh_terms: D002352:Carrier Proteins / Q000235:genetics; D004247:DNA / Q000235:genetics; D004260:DNA Repair; D004269:DNA, Bacterial / Q000528:radiation effects; D004268:DNA-Binding Proteins; D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000187:drug effects / Q000528:radiation effects*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D011995:Recombination, Genetic; D014466:Ultraviolet Rays
chemical_list: D002352:Carrier Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D004247:DNA; D006861:Hydrogen Peroxide