Role of G-->T transversions in the mutagenicity of alkylperoxyl radicals: induction of alkali-labile sites in bacteriophage M13mp19.
The mutagenicity of peroxyl radicals, ubiquitous products of lipid peroxidation, was assessed using an in vitro M13 forward mutational assay. Single-stranded M13mp19 plasmids were incubated with a range of concentrations of the azo initiator 2,2'-azobis(2-amidinopropane) hydrochloride, and then transfected into competent, SOS-induced Escherichia coli JM105 cells. Incubation with peroxyl radicals produced a concentration-dependent decrease in phage survival, with a 500 microM concentration of the azo initiator reducing the transfection efficiency by more than 90% while inducing a corresponding 6-fold increase in lacZ alpha mutation frequencies. Peroxyl radical-induced mutagenesis was completely prevented by the peroxyl radical scavenger Trolox. Automated DNA sequence analysis of the lacZ alpha gene of 100 peroxyl radical-induced mutants revealed that the most frequent sequence changes were base pair substitutions (92/95), with G-->T transversions predominating (73/92). Alkaline treatment prior to transfection diminished the mutagenicity of damaged plasmids to a level resembling that of unmodified DNA. While abasic sites might account for the sensitivity to alkaline cleavage, the possibility that unidentified nonabasic alkaline-labile lesions also contribute to peroxyl radical mutagenesis cannot be excluded. Collectively, these findings raise the possibility that DNA damage caused by a major class of endogenous radicals contributes to one of the most common spontaneous mutational events, the G-->T transversion.
Harkin
L A
LA
Department of Clinical and Experimental Pharmacology, The University of Adelaide, South Australia.
Butler
L M
LM
Burcham
P C
PC
D000468:Alkalies / Q000633:toxicity*; D000578:Amidines / Q000633:toxicity; D017104:Bacteriophage M13 / Q000187:drug effects / Q000235:genetics*; D001483:Base Sequence; D004279:DNA, Viral / Q000187:drug effects; D016166:Free Radical Scavengers / Q000633:toxicity; D006801:Humans; D015227:Lipid Peroxidation / Q000235:genetics; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000187:drug effects; D009153:Mutagens / Q000633:toxicity*; D010545:Peroxides / Q000633:toxicity*; D017354:Point Mutation
D000468:Alkalies; D000578:Amidines; D004279:DNA, Viral; D016166:Free Radical Scavengers; D009153:Mutagens; D010545:Peroxides; C049375:perhydroxyl radical; C046728:2,2'-azobis(2-amidinopropane)