Delayed Colony Formation in Diploid Cells of Various Genotypes after UV Light Irradiation

Abstract

Experimental curves of the dependence of survival and delayed colony formation on UV light (254 nm) fluence for two wild-type strains of diploid yeast Saccharomyces cerevisiae capable of recovering from UV damage and their UV-sensitive mutants are presented. The dose–response curves were sigmoid for wild-type cells and rad6/rad6 and rad18/rad18 mutants, which were sensitive to UV irradiation by a factor of 2.2 and 1.5 for survival and 2.0 and 3.1 for delayed colony formation in comparison with the original strain (XS800). The T2 (rad2/rad2) strain was characterized by an exponential dose–response curve and was more sensitive to UV irradiation by a factor of 10.7 for survival and 7.0 for delayed colony formation compared to the original strain (T1). Delayed colony formation of all studied strains reached 100% with increasing UV light fluence. Unlike traditional representations, these data indicate that the delayed colony formation is mainly determined by cell ploidy and does not depend on the shape of the dose–response curves and UV sensitivity of cells.