Influence of SOS repair on the specificity of radiation mutagenesis in bacteriophage phiX174.

The ochre mutant oc9 of bacteriophage phiX174 was irradiated with gamma-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 gamma-irradiated phiX174 was subjected to W-mutagenesis. For oc9 gamma-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 phiX174 showed a similar phenomenon. These results suggest that the specificity with regard to insertion of bases opposite radiation damage in phiX174 DNA is different for host cells in which SOS repair has been induced and cells in which SOS repair is not operative.