To study the kinetics of UV-induced gene and chromosome mutations in the yeast S. cerevisiae, several genetic assays were used. We treated yeast cells with UV light of up to 130 J/m². UV irradiation induced all types of base substitutions, although transitions — in particular, GC-AT events — were predominant. Frameshift mutations were induced at the same frequency as the base pair substitution GC-AT, while forward mutations in the CAN1 gene exceeded the more expressive base pair substitutions by about an order of magnitude. Chromosome mutations were the most efficient. The kinetic of the induced gene and chromosome mutations is represented by a linear-quadratic function. Such curves have been reported for UV mutagenesis in bacteria and they have been explained by the induction of SOS error-prone repair. Similar biphasic kinetics was described for yeast in our work. These data suggest the occurrence of several factors forming the mutagenic response of eukaryotic cells to UV light.

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