title: Double-strand breaks trigger MRX- and Mec1-dependent, but Tel1-independent, checkpoint activation.
abstract: Together with the Tel1 PI3 kinase, the Mre11/Rad50/Xrs2 (MRX) complex is involved in checkpoint activation in response to double-strand breaks (DSBs), a function also conserved in human cells by Mre11/Rad50/Nbs1 acting with ATM. It has been proposed that the yeast Tel1/MRX pathway is activated in the presence of DSBs that cannot be resected. The Mec1 PI3 kinase, by contrast, would be involved in detecting breaks that can be processed. The significance of a Mec1/MRX DSB-activated DNA damage checkpoint has yet to be reported. To understand whether the MRX complex works specifically with Tel1 or Mec1, we investigated MRX function in checkpoint activation in response to endonuclease-induced DSBs in synchronized cells. We found that the expression of EcoRI activated the G1 and intra-S phase checkpoints in a MRX- and Mec1-dependent, but Tel1-independent manner. The pathways identified here are therefore different from the Tel1/MRX pathway that was previously reported. Thus, our results demonstrate that MRX can function in concert with both Mec1 and Tel1 PI3K-like kinases to trigger checkpoint activation in response to DSBs. Importantly, we also describe a novel MRX-independent checkpoint that is activated in late S-phase when cells replicate their DNA in the presence of DSBs. The existence of this novel mode of checkpoint activation explains why several previous studies had reported that mutations in the MRX complex did not abrogate DSB-induced checkpoint activation in asynchronous cells.
authors.affiliation: Wellcome Trust and Cancer Research UK Gurdon Institute, Cambridge UK. muriel.grenon@nuigalway.ie
authors.forename: Muriel
authors.initials: M
authors.lastname: Grenon
authors.forename: Christine P
authors.initials: CP
authors.lastname: Magill
authors.forename: Noel F
authors.initials: NF
authors.lastname: Lowndes
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Jackson
mesh_terms: D002453:Cell Cycle; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000502:physiology*; D015246:Deoxyribonuclease EcoRI / Q000494:pharmacology; D004706:Endodeoxyribonucleases / Q000502:physiology*; D005090:Exodeoxyribonucleases / Q000502:physiology*; D005656:Fungal Proteins / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D017346:Protein Serine-Threonine Kinases; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; C086930:RAD50 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C086929:XRS2 protein, S cerevisiae; C088937:MEC1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; C513623:TEL1 protein, S cerevisiae; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; C094191:MRE11 protein, S cerevisiae; D015246:Deoxyribonuclease EcoRI