Influence of SOS repair on the specificity of radiation mutagenesis in bacteriophage ϕX174

Abstract
Summary The ochre mutant oc9 of bacteriophage ϕX174 was irradiated with γ-rays and the revertants were assayed on unirradiated and UV-irradiated host bacteria carrying an amber suppressor. The yield of revertants (amber+wild type) was higher on UV-irradiated than on unirradiated bacteria, showing that γ-irradiated ϕX174 was subjected to W-mutagenesis. For oc9 γ-irradiated in the presence of oxygen the fraction of amber mutants among the revertants was lower when mutants were scored on UV-irradiated bacteria than when assayed on unirradiated indicator cells. The same fraction of ambers was obtained when mutants were assayed on unirradiated and UV-irradiated samples of a recA indicator strain. UV-irradiated ϕX174 showed a similar phenomenon. These results suggest that the specificity with regard to insertion of bases opposite radiation damage in ϕX174 DNA is different for host cells in which SOS repair has been induced and cells in which SOS repair is not operative.