Abstract
When mutation spectrum of haploid yeast cell is analyzed, various point mutations are detectable. On the other hand, when mutations of heterozygous locus from diploid cells are analyzed, allelic loss from functional counterpart is frequently observed. The event is referred to as loss of heterozygosity (LOH). LOH is caused by mitotic recombination between homologous chromosomes. Mitotic recombination functions as one of the DNA damage tolerant mechanism. The purpose of this study is to investigate the process of DNA damage repair by characterizing the mechanism of UV-induced LOH. To study the source of LOH events, we have constructed CAN1/can1 diploid yeast strains and examined canavanine-resistance (CanR) mutations to can1/can1. The damage on the chromosome carrying CAN1 induced more CanR mutants than the damage chromosome carrying can1, and a significant increase in CanR mutants were observed when the damage were induced during DNA replication. These results indicate that mitotic recombination, that functions as DNA damage tolerant mechanism, occurs through a nonreciprocal strand transfer associated with DNA replication.
