EFFECTS OF THE CDC2 GENE ON ADAPTIVE MUTATION IN THE YEAST SACCHAROMYCES-CEREVISIAE

We have studied the influence of a temperature-senstitive cdc2-1 mutation in DNA polymerase delta on the selection-induced mutation occurring at the LYS-2 locus in the yeast Saccharomyces cerevisiae. It was found that in cells plated on synthetic complete medium lacking only lysine, the numbers of Lys(+) revertant colonies accumulated in a time-dependent manner in the absence of any detectable increase in cell number. When cdc2-1 mutant cells, after selective plating, were incubated at the restrictive temperature of 37 degrees C for 5 h daily for 7 days, the frequency of an adaptive reversion of lys(-) --> Lys(+) was significantly higher than the frequency in cells incubated only at the permissive temperature, or in wild-type cells incubated either at 23 degrees C or 37 degrees C. Therefore, when the proofreading activity of DNA polymerase delta is impaired under restrictive conditions, the frequency of adaptive mutations is markedly enhanced.