title: Regulation of homologous integration in yeast by the DNA repair proteins Ku70 and RecQ.
abstract: The product of the BLM gene, which is mutated in Bloom syndrome in humans, and the Saccharomyces cerevisiae protein Sgs1 are both homologous to the Escherichia coli DNA helicase RecQ, and have been shown to be involved in the regulation of homologous recombination. Mutations in these genes result in genome instability because they increase the incidence of deletions and translocations. We present evidence for a genetic interaction between SGS1 and YKU70, which encodes the S. cerevisiae homologue of the human DNA helicase Ku70. In a yku70 mutant background, sgs1 mutations increased sensitivity to DNA breakage induced either by treatment with camptothecin or by the expression of the restriction enzyme EcoRI. The yku70 mutation caused a fourfold increase in the rate of double-strand break (DSB)-induced target integration as that seen in the sgs1 mutant. The combination of yku70 and sgs1 mutations additively increased the rate of the targeted integration, and this effect was completely suppressed by deletion of RAD51. Interestingly, an extra copy of YKU70 partially suppressed the increase in targeted integration seen in the sgs1 single mutant. These results suggest that Yku70 modulates the repair of DSBs associated with homologous recombination in a different way from Sgs1, and that the inactivation of RecQ and Ku70 homologues may enhance the frequency of gene targeting in higher eukaryotes.
authors.affiliation: Department of Biological Functions and Engineering, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu-ku, Kitakyushu, 808-0196, Japan.
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Yamana
authors.forename: Toshinari
authors.initials: T
authors.lastname: Maeda
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohba
authors.forename: Takehiko
authors.initials: T
authors.lastname: Usui
authors.forename: Hiroaki I
authors.initials: HI
authors.lastname: Ogawa
authors.forename: Kohji
authors.initials: K
authors.lastname: Kusano
mesh_terms: D002166:Camptothecin; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018390:Gene Targeting / Q000379:methods; D042822:Genomic Instability / Q000235:genetics*; D009154:Mutation / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D053484:RecQ Helicases; D011995:Recombination, Genetic / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; C520769:YKU70 protein, S cerevisiae; C081647:high affinity DNA-binding factor, S cerevisiae; C090472:SGS1 protein, S cerevisiae; D004265:DNA Helicases; D053484:RecQ Helicases; D002166:Camptothecin