title: Rad51-dependent DNA structures accumulate at damaged replication forks in sgs1 mutants defective in the yeast ortholog of BLM RecQ helicase.
abstract: S-phase cells overcome chromosome lesions through replication-coupled recombination processes that seem to be assisted by recombination-dependent DNA structures and/or replication-related sister chromatid junctions. RecQ helicases, including yeast Sgs1 and human BLM, have been implicated in both replication and recombination and protect genome integrity by preventing unscheduled mitotic recombination events. We have studied the RecQ helicase-mediated mechanisms controlling genome stability by analyzing replication forks encountering a damaged template in sgs1 cells. We show that, in sgs1 mutants, recombination-dependent cruciform structures accumulate at damaged forks. Their accumulation requires Rad51 protein, is counteracted by Srs2 DNA helicase, and does not prevent fork movement. Sgs1, but not Srs2, promotes resolution of these recombination intermediates. A functional Rad53 checkpoint kinase that is known to protect the integrity of the sister chromatid junctions is required for the accumulation of recombination intermediates in sgs1 mutants. Finally, top3 and top3 sgs1 mutants accumulate the same structures as sgs1 cells. We suggest that, in sgs1 cells, the unscheduled accumulation of Rad51-dependent cruciform structures at damaged forks result from defective maturation of recombination-dependent intermediates that originate from the replication-related sister chromatid junctions. Our findings might contribute to explaining some of the recombination defects of BLM cells.
authors.affiliation: F.I.R.C. Institute of Molecular Oncology Foundation, 20141, Milan, Italy. giordano.liberi@ifom-ieo-campus.it
authors.forename: Giordano
authors.initials: G
authors.lastname: Liberi
authors.forename: Giulio
authors.initials: G
authors.lastname: Maffioletti
authors.forename: Chiara
authors.initials: C
authors.lastname: Lucca
authors.forename: Irene
authors.initials: I
authors.lastname: Chiolo
authors.forename: Anastasia
authors.initials: A
authors.lastname: Baryshnikova
authors.forename: Cecilia
authors.initials: C
authors.lastname: Cotta-Ramusino
authors.forename: Massimo
authors.initials: M
authors.lastname: Lopes
authors.forename: Achille
authors.initials: A
authors.lastname: Pellicioli
authors.forename: James E
authors.initials: JE
authors.lastname: Haber
authors.forename: Marco
authors.initials: M
authors.lastname: Foiani
mesh_terms: D000251:Adenosine Triphosphatases / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D004265:DNA Helicases / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D051135:Rad51 Recombinase; D053484:RecQ Helicases; D029701:Saccharomyces cerevisiae Proteins; D015003:Yeasts / Q000235:genetics / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D004247:DNA; D051135:Rad51 Recombinase; D000251:Adenosine Triphosphatases; C506725:RECQL protein, human; C090472:SGS1 protein, S cerevisiae; D004265:DNA Helicases; D053484:RecQ Helicases