Indications for an inducible component of error-prone DNA repair in yeast.

In a thermoconditional mutant of mutagenic DNA repair (rev2(ts) = rad5-8) of Saccharomyces cerevisiae, recovery of survival and mutation frequencies can be monitored by incubating UV-irradiated cells in growth medium at a permissive temperature (23°C) before plating and a shift to restrictive temperature (36°C). Inhibition of protein synthesis with cycloheximide during incubation at permissive conditions blocks this REV2 dependent recovery process in stationary phase rev2(ts) cells, whereas it can be reduced but not totally abolished in exponentially growing cells. These results indicate a strict dependence on post-irradiation protein synthesis in stationary phase cells and argue for a considerable constitutive level and only limited inducibility in logarithmic phase cells. The UV inducibility of the REV2 coded function in stationary phase cells could be confirmed by analysis of the dose-response pattern of the his 5-2 reversion: in stationary phase rev2(ts) cells, the quadratic component of the biphasic linear-quadratic induction kinetics found at 23°C, which is interpreted as the consequence of induction of mutagenic repair, is eliminated at 36°C