Positive and negative roles of homologous recombination in the maintenance of genome stability in Saccharomyces cerevisiae.
In previous studies of the loss of heterozygosity (LOH), we analyzed a hemizygous URA3 marker on chromosome III in S. cerevisiae and showed that homologous recombination is involved in processes that lead to LOH in multiple ways, including allelic recombination, chromosome size alterations, and chromosome loss. To investigate the role of homologous recombination more precisely, we examined LOH events in rad50 Delta, rad51 Delta, rad52 Delta, rad50 Delta rad52 Delta, and rad51 Delta rad52 Delta mutants. As compared to Rad(+) cells, the frequency of LOH was significantly increased in all mutants, and most events were chromosome loss. Other LOH events were differentially affected in each mutant: the frequencies of all types of recombination were decreased in rad52 mutants and enhanced in rad50 mutants. The rad51 mutation increased the frequency of ectopic but not allelic recombination. Both the rad52 and rad51 mutations increased the frequency of intragenic point mutations approximately 25-fold, suggesting that alternative mutagenic pathways partially substitute for homologous recombination. Overall, these results indicate that all of the genes are required for chromosome maintenance and that they most likely function in homologous recombination between sister chromatids. In contrast, other recombination pathways can occur at a substantial level even in the absence of one of the genes and contribute to generating various chromosome rearrangements.
Department of Molecular Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan. umeza@bs.aist-nara.ac.jp
Jumpei
J
Yoshida
Keiko
K
Umezu
Hisaji
H
Maki
D004268:DNA-Binding Proteins / Q000235:genetics; D005819:Genetic Markers; D042822:Genomic Instability; D019656:Loss of Heterozygosity; D017354:Point Mutation; D051135:Rad51 Recombinase; D051721:Rad52 DNA Repair and Recombination Protein; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics
D004268:DNA-Binding Proteins; D005819:Genetic Markers; C086930:RAD50 protein, S cerevisiae; C497197:RAD52 protein, S cerevisiae; D051721:Rad52 DNA Repair and Recombination Protein; D029701:Saccharomyces cerevisiae Proteins; C495151:RAD51 protein, S cerevisiae; D051135:Rad51 Recombinase