Radiation-induced mitotic gene conversion frequency in yeast in modulated by the conditions allowing DNA double-strand break repair

Abstract

Repair of DNA double-strand breaks (DSB)_involves recombinational process which may lead to gene conversion (intragenic recombination). Using the diploid yeast mutant rad54-3 heteroallelic for his1 (his1-7/his1-1) and temperature conditional for DSB rejoining, radiation induced gene conversion was investigated as dependent on DSB rapair under different postirradiation conditions. Gene conversion is negligible under conditions preventing DSB repair (36°C). In contrast, gene conversion is observed when cells are incubated at the permissive temperature (23°C) both under growth and nongrowth condtions. However, there is a much higher yield of convertants for cells incubated under growth as opposed to nongrowth conditions. These results can most plausibly be explained by the cell cycle regulated enhancement of the expression of genes such as PMS and POL3 known to be involved in gene conversion processes and/or the enhanced recombination in transcriptionally active genes. ‘Nutrient stress’ inducible responses and/or cell specific recombination pathways leading to gene conversion events preferentially in S-phase cells seem to be less likely.