Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.
Curr Biol. 2012 May 22;22(10):900-6. doi: 10.1016/j.cub.2012.03.052. Epub 2012 Apr 19.
Kinetochores are the macromolecular complexes that interact with microtubules to mediate chromosome segregation. Accurate segregation requires that kinetochores make bioriented attachments to microtubules from opposite poles. Attachments between kinetochores and microtubules are monitored by the spindle checkpoint, a surveillance system that prevents anaphase until every pair of chromosomes makes proper bioriented attachments. Checkpoint activity is correlated with the recruitment of checkpoint proteins to the kinetochore. Mps1 is a conserved protein kinase that regulates segregation and the spindle checkpoint, but few of the targets that mediate its functions have been identified. Here, we show that Mps1 is the major kinase activity that copurifies with budding yeast kinetochore particles and identify the conserved Spc105/KNL-1/blinkin kinetochore protein as a substrate. Phosphorylation of conserved MELT motifs within Spc105 recruits the Bub1 protein to kinetochores, and this is reversed by protein phosphatase I (PP1). Spc105 mutants lacking Mps1 phosphorylation sites are defective in the spindle checkpoint and exhibit growth defects. Together, these data identify Spc105 as a key target of the Mps1 kinase and show that the opposing activities of Mps1 and PP1 regulate the kinetochore localization of the Bub1 protein.
着丝粒是与微管相互作用以介导染色体分离的大分子复合物。准确的分离需要着丝粒与来自相反极的微管形成双取向附着。着丝粒和微管之间的附着由纺锤体检查点监测,这是一种防止后期发生的监控系统,直到每对染色体都形成适当的双取向附着。检查点活性与检查点蛋白在着丝粒上的募集相关。Mps1 是一种保守的蛋白激酶,可调节有丝分裂和纺锤体检查点,但介导其功能的靶点很少被鉴定。在这里,我们表明 Mps1 是与芽殖酵母着丝粒颗粒共纯化的主要激酶活性,并鉴定出保守的 Spc105/KNL-1/blinkin 着丝粒蛋白作为底物。Spc105 内保守的 MELT 模体的磷酸化将 Bub1 蛋白招募到着丝粒上,这被蛋白磷酸酶 I (PP1) 逆转。缺乏 Mps1 磷酸化位点的 Spc105 突变体在纺锤体检查点中存在缺陷,并且表现出生长缺陷。总之,这些数据将 Spc105 鉴定为 Mps1 激酶的关键靶标,并表明 Mps1 和 PP1 的相反活性调节了 Bub1 蛋白在着丝粒上的定位。