title: Mutational spectrum analysis of umuC-independent and umuC-dependent gamma-radiation mutagenesis in Escherichia coli.
abstract: gamma-Radiation mutagenesis (oxic versus anoxic) was examined in wild-type, umuC and recA strains of Escherichia coli K-12. Mutagenesis [argE3(Oc)----Arg+] was blocked in a delta (recA-srlR)306 strain at the same doses that induced mutations in umuC122::Tn5 and wild-type strains, indicating that both umuC-independent and umuC-dependent mechanisms function within recA-dependent misrepair. Analyses of various suppressor and back mutations that result in argE3 and hisG4 ochre reversion and an analysis of trpE9777 (+1 frameshift) reversion were performed on umuC and wild-type cells irradiated in the presence and absence of oxygen. While the umuC strain showed the gamma-radiation induction of base substitution and frameshifts when irradiated in the absence of oxygen, the umuC mutation blocked all oxygen-dependent base-substitution mutagenesis, but not all oxygen-dependent frameshift mutagenesis. For anoxically irradiated cells, the yields of GC----AT [i.e., at the supB and supE (Oc) loci] and AT----GC transitions (i.e., at the argE3 and hisG4 loci) were essentially umuC independent, while the yields of (AT or GC)----TA transversions (i.e., at the supC, supL, supM, supN and supX loci) were heavily umuC dependent. These data suggest new concepts about the nature of the DNA lesions and the mutagenic mechanisms that lead to gamma-radiation mutagenesis.
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, CA 94305.
authors.forename: N J
authors.initials: NJ
authors.lastname: Sargentini
authors.forename: K C
authors.initials: KC
authors.lastname: Smith
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000235:genetics*; D001482:Base Composition; D003062:Codon / Q000235:genetics; D004260:DNA Repair; D004269:DNA, Bacterial / Q000235:genetics / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000235:genetics / Q000528:radiation effects*; D005720:Gamma Rays; D005798:Genes, Bacterial / Q000528:radiation effects; D005838:Genotype; D009154:Mutation; D013489:Suppression, Genetic / Q000528:radiation effects
chemical_list: D001426:Bacterial Proteins; D003062:Codon; D004269:DNA, Bacterial