Radiation-induced base substitution mutagenesis in single-stranded DNA phage M13

Abstract

Radiation-induced mutagenesis of Escherichia coli depends on the ability of the bacteria to perform error-prone repair^1,2. This SOS repair activity is induced by irradiation of bacteria and gives rise to mutations both at the site of radiation-induced lesions (targeted mutations) and in undamaged DNA (untargeted mutations)^1,3–6. To elucidate the relative contributions of targeted and untargeted mutations to γ and UV radiation mutagenesis we have determined the DNA sequences of 174 M13 revertant phages isolated from stocks of irradiated or unirradiated amber mutants grown in irradiated (SOS-induced) or unirradiated (non-induced) host bacteria. As reported here, differences in the spectra of base change mutations induced in the various conditions were apparent, but we detected no obvious specificity of mutagenesis. In particular, in our conditions, pyrimidine dimers did not seem to be the principal sites of UV-induced base substitution mutagenesis, suggesting that such mutagenesis occurs at the sites of lesions other than pyrimidine dimers, or is untargeted.