Mitochondrial DNA synthesis in non-growth condition (liquid holding) in Saccharomyces cerevisiae. Relation with growth stages and mitochondrial DNA repair after UV-irradiation

The synthesis of DNA as measured by incorporation of [14C]adenine in Saccharomyces cerevisiae liquid held in non-growth conditions was followed in controls and UV-irradiated cells. The incorporation into mitochondrial DNA relative to total DNA was higher in these conditions than that observed in growth medium, especially in liquid held stationary phase cells. The absolute amount of mitochondrial DNA synthesized during liquid holding was larger in exponential than in stationary phase cells and increased after UV-irradiation. The data reported are discussed in relation to the effects of liquid holding on the UV-induction of rho- mutants, such effects depending upon the growth stage of the cells at the time of irradiation. A correlation has been found between the initial ability of the cells to synthesize mitochondrial DNA in liquid holding conditions and their capacity to repair UV-induced lesions in this DNA. A hypothesis is proposed that the opposite effects of liquid holding on the UV-induction of rho- mutants observed in exponential versus stationary phase cells are not due to the action of different repair pathways, but result essentially from quantitative differences in mtDNA synthesis. (author)