Induced recombination and reversion of the CDC8 gene in relation to the cell cycle of yeast

The induction of mitotic recombination in the CDC8 locus was studied in a diploid strain heteroallelic for cdc8 mutations (cdc8-1/cdc8-3); mitotic reversion was studied in strains cdc8-1/cdc8-1 and cdc8-3/cdc8-3. Conversion and reversion did not occur in those cells blocked at the S stage of the cell cycle by exposure to a nonpermissive temperature. In stationary phase cells irradiated just prior to exposure to temperature stress, the induction of recombinants was rather low and the induction of revertants was minimal. Conversely, a significant induction of cdc+ occurred in logarithmic phase cells subjected to the same treatment. Irradiation of synchronously dividing cultures revealed that intragenic recombination occurs at all three stages of the cell cycle-G1, S and G2. It was also found that UV-induced gene reversion can occur during the S and G2 stages, but not during the G1 stage of the cell cycle.