MUTATIONS IN THE MUTY GENE OF ESCHERICHIA-COLI ENHANCE THE FREQUENCY OF TARGETED G-C-]T-A TRANSVERSIONS INDUCED BY A SINGLE 8-OXOGUANINE RESIDUE IN SINGLE-STRANDED-DNA

Oxidative damage to guanine in DNA results in the formation of 8-oxoguanine, which has been shown to induce G --> T transversions targeted to this site. The mutagenicity of this lesion was studied in several mutator strains of Escherichia coli, using single-stranded DNA containing a single 8-oxoguanine residue. The frequencies of targeted G --> T transversions increased markedly in mut Y strains, while this mutagenic event was not affected in mutM or mutS strains. Introdution of a mutM mutation into a mut Y strain caused a somewhat higher frequency of G --> T transversions than that in the mutY strain and the effect of a mutS mutation was marginal. We conclude that the mutY gene plays a crucial role in preventing targeted G --> T mutations derived from misreplication of the 8-oxoguanine-containing template DNA.