Problems in the estimation of mutation rates and in the detection of induced mutations in man

The contribution of nuclear-directed protein synthesis in the repair of lethal and mitochondrial genetic damage after UV-irradiation of exponential and stiationary phase haploid yeast cells was examined. This was carried out using cycloheximide (CH), a specific inhibitor of nuclear protein synthesis. It appears that nuclear protein synthesis required for the increase in survival seen after the liquid holding of cells at both stages, as well as for the “petite” recovery seen after the liquid holding of exponential phase cells. The characteristic negative liquid holding effect observed for the UV induction of “petites” in stationary phase cells (increase of the frequency of “petites” during storage) remained following all the treatments which inhibited nuclear protein synthesis. However, the application of photoreactivating light following dark holding with cycloheximide indicates that some steps of the repair of both nuclear and mitochondrial damage are performed in the absence of a synthesis of proteins.