The yeast Xrs2 complex functions in S phase checkpoint regulation.
The Nbs1 complex is an evolutionarily conserved multisubunit nuclease composed of the Mre11, Rad50, and Nbs1 proteins. Hypomorphic mutations in the NBS1 or MRE11 genes in humans result in conditions characterized by DNA damage sensitivity, cell cycle checkpoint deficiency, and high cancer incidence. The equivalent complex in the yeast Saccharomyces cerevisiae (Xrs2p complex) has been implicated in DNA double-strand break repair and in telomere length regulation. Here, we find that xrs2Delta, mre11Delta, and rad50Delta mutants are markedly defective in the initiation of the intra-S phase checkpoint in response to DNA damage. Furthermore, the absence of a functional Xrs2p complex leads to sensitivity to deoxynucleotide depletion and to an inability to efficiently slow down cell cycle progression in response to hydroxyurea. The checkpoint appears to require the nuclease activity of Mre11p and its defect is associated with the abrogation of the Tel1p/Mec1p signaling pathway. Notably, DNA damage induces phosphorylation of both Xrs2p and Mre11p in a Tel1p-dependent manner. These results indicate that the Tel1p/ATM signaling pathway is conserved from yeast to humans and suggest that the Xrs2p/Nbs1 complexes act as signal modifiers.
D'Amours
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Wellcome Trust and Cancer Research Campaign Institute of Cancer and Developmental Biology, and Department of Zoology, University of Cambridge, CB2 1QR Cambridge, UK.
Jackson
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D001761:Bleomycin / Q000494:pharmacology; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D002469:Cell Separation; D064447:Checkpoint Kinase 2; D004249:DNA Damage; D004260:DNA Repair; D004305:Dose-Response Relationship, Drug; D004706:Endodeoxyribonucleases; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004843:Epistasis, Genetic; D005090:Exodeoxyribonucleases; D005434:Flow Cytometry; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D005838:Genotype; D006918:Hydroxyurea / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D009154:Mutation; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D016196:S Phase / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000737:chemistry* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D015398:Signal Transduction; D013997:Time Factors
D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D029701:Saccharomyces cerevisiae Proteins; C086929:XRS2 protein, S cerevisiae; D001761:Bleomycin; D064447:Checkpoint Kinase 2; D017346:Protein Serine-Threonine Kinases; C513623:TEL1 protein, S cerevisiae; C067022:RAD53 protein, S cerevisiae; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; C094191:MRE11 protein, S cerevisiae; D006918:Hydroxyurea