INFLUENCE OF SOS REPAIR ON THE SPECIFICITY OF RADIATION MUTAGENESIS IN BACTERIOPHAGE PHI-X174

The ochre mutant oc9 of bacteriophage φ{symbol}X174 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 φ{symbol}X174 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 φ{symbol}X174 showed a similar phenomenon. These results suggest that the specificity with regard to insertion of bases opposite radiation damage in φ{symbol}X174 DNA is different for host cells in which SOS repair has been induced and cells in which SOS repair is not operative. © 1979 Springer-Verlag.