title: Fission yeast RecQ helicase Rqh1 is required for the maintenance of circular chromosomes.
abstract: Protection of telomeres protein 1 (Pot1) binds to single-stranded telomere overhangs and protects chromosome ends. RecQ helicases regulate homologous recombination at multiple stages, including resection, strand displacement, and resolution. Fission yeast pot1 and RecQ helicase rqh1 double mutants are synthetically lethal, but the mechanism is not fully understood. Here, we show that the synthetic lethality of pot1Δ rqh1Δ double mutants is due to inappropriate homologous recombination, as it is suppressed by the deletion of rad51(+). The expression of Rad51 in the pot1Δ rqh1Δ rad51Δ triple mutant, which has circular chromosomes, is lethal. Reduction of the expression of Rqh1 in a pot1 disruptant with circular chromosomes caused chromosome missegregation, and this defect was partially suppressed by the deletion of rad51(+). Taken together, our results suggest that Rqh1 is required for the maintenance of circular chromosomes when homologous recombination is active. Crossovers between circular monomeric chromosomes generate dimers that cannot segregate properly in Escherichia coli. We propose that Rqh1 inhibits crossovers between circular monomeric chromosomes to suppress the generation of circular dimers.
authors.affiliation: Department of Molecular Biotechnology, Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Nanbu
authors.forename: Katsunori
authors.initials: K
authors.lastname: Takahashi
authors.forename: Johanne M
authors.initials: JM
authors.lastname: Murray
authors.forename: Naoya
authors.initials: N
authors.lastname: Hirata
authors.forename: Shinobu
authors.initials: S
authors.lastname: Ukimori
authors.forename: Mai
authors.initials: M
authors.lastname: Kanke
authors.forename: Hisao
authors.initials: H
authors.lastname: Masukata
authors.forename: Masashi
authors.initials: M
authors.lastname: Yukawa
authors.forename: Eiko
authors.initials: E
authors.lastname: Tsuchiya
authors.forename: Masaru
authors.initials: M
authors.lastname: Ueno
mesh_terms: D016923:Cell Death / Q000235:genetics; D015825:Chromosomes, Fungal / Q000235:genetics* / Q000378:metabolism; D004265:DNA Helicases / Q000235:genetics* / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D059765:Homologous Recombination / Q000235:genetics*; D009154:Mutation; D051135:Rad51 Recombinase / Q000235:genetics / Q000378:metabolism; D012568:Schizosaccharomyces / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics* / Q000378:metabolism; D000089804:Shelterin Complex; D016615:Telomere / Q000235:genetics / Q000378:metabolism; D034501:Telomere-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D029702:Schizosaccharomyces pombe Proteins; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins; C499082:pot1 protein, S pombe; D051135:Rad51 Recombinase; D004265:DNA Helicases; C106462:Rqh1 protein, S pombe; D004264:DNA Topoisomerases, Type I