UV-induced mitotic recombination and its dependence on photoreactivation and liquid holding in the rad6-1 mutant of Saccharomyces cerevisiae.

Spontaneous and UV-induced mitotic recombination was compared in diploids homozygous for rad6-1 mutation and in the wild-type strain carrying heterozygous markers for detecting gene conversion (hom2-1, hom2-2) and crossing over (ade1, ade2). Diploids homozygous for rad6-1 mutation were characterised by an elevated level of spontaneous and UV-induced mitotic recombination, particularly the intergenic events. Exposure of UV-irradiated strains to visible light resulted in an increased survival and decreased level of mitotic recombination. Liquid holding (LH) differentially affected frequency of mitotic intergenic and intragenic recombination in mutant and wild-type strains, being without any significant effect on cell survival. In a mutant strain intragenic recombination is significantly increased, intergenic only slightly. In the wild-type strain intragenic recombination is slightly decreased but intergenic is not changed by LH. Visible light applied after LH had no effect on survival and mitotic recombination in the wild type, while in the mutant strain photoreactivability of survival was fully preserved and accompanied by a decrease in the frequency of intragenic and intergenic recombination. The results suggest that metabolic pathways responsible for restoring cell survival are independent of or only partly overlapping with those concerning recombination events.