Genetic effects of methylmethanesulphonate during meiosis in Saccharomyces cerevisiae.

Enhanced mutagenic action after methylmethanesulphonate (MMS) treatment was found in pre-replicative meiotic yeast cells of the strain D7. The level of gene conversion after MMS treatment rose above the spontaneous level during the period of commitment to meiotic recombination, but at later times into meiosis became indistinguishable from the full meiotic level. In contrast reciprocal recombination detected between ade 2 and the centromere of chromosome XV after MMS treatment remained above the spontaneous level up to commitment to meiotic cell division with relatively high levels through meiotic prophase I. These results are discussed in relation to MMS-induced damage and its repair, particularly double-strand break repair.