title: Dpb11 coordinates Mec1 kinase activation with cell cycle-regulated Rad9 recruitment.
abstract: Eukaryotic cells respond to DNA damage by activating checkpoint signalling pathways. Checkpoint signals are transduced by a protein kinase cascade that also requires non-kinase mediator proteins. One such mediator is the Saccharomyces cerevisiae Dpb11 protein, which binds to and activates the apical checkpoint kinase, Mec1. Here, we show that a ternary complex of Dpb11, Mec1 and another key mediator protein Rad9 is required for efficient Rad9 phosphorylation by Mec1 in vitro, and for checkpoint activation in vivo. Phosphorylation of Rad9 by cyclin-dependent kinase (CDK) on two key residues generates a binding site for tandem BRCT repeats of Dpb11, and is thereby required for Rad9 recruitment into the ternary complex. Checkpoint signalling via Dpb11, therefore, does not efficiently occur during G1 phase when CDK is inactive. Thus, Dpb11 coordinates checkpoint signal transduction both temporally and spatially, ensuring the initiator kinase is specifically activated in proximity of one of its critical substrates.
authors.affiliation: Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Hertfordshire, UK.
authors.forename: Boris
authors.initials: B
authors.lastname: Pfander
authors.forename: John F X
authors.initials: JF
authors.lastname: Diffley
mesh_terms: D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D047908:Intracellular Signaling Peptides and Proteins; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis*; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000201:enzymology; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis* / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D018797:Cell Cycle Proteins; C097185:DPB11 protein, S cerevisiae; D047908:Intracellular Signaling Peptides and Proteins; D029701:Saccharomyces cerevisiae Proteins; C069930:rad9 protein; C088937:MEC1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases