Stationary-phase mutations in proofreading exonuclease-deficient strains of the yeast Saccharomyces cerevisiae.

In order to understand the role of yeast polymerases in spontaneous mutagenesis in non-growing cells we have studied the effects of mutations that impair the 3'--> 5' exonuclease function of polymerases delta (pol3-01) and epsilon (pol2-4) on the spontaneous reversion frequency of the frameshift mutation his7-2 in cells starved for histidine. We showed that for each exonuclease-deficient mutant the rate of reversion per viable cell per day observed in stationary-phase cells remained constant up to the 9th day of starvation (while the number of viable cells dropped), and was very similar to that observed in the same mutants during the growth phase. These data suggest that both DNA polymerases are involved in the control of mutability in non-growing cells.