Howard Hughes Medical Institute, Vanderbilt University School of Medicine, Nashville, TN 37212, USA.
J Cell Biol. 2011 Nov 14;195(4):583-93. doi: 10.1083/jcb.201105074. Epub 2011 Nov 7.
Cdk1 controls many aspects of mitotic chromosome behavior and spindle microtubule (MT) dynamics to ensure accurate chromosome segregation. In this paper, we characterize a new kinetochore substrate of fission yeast Cdk1, Nsk1, which promotes proper kinetochore-MT (k-MT) interactions and chromosome movements in a phosphoregulated manner. Cdk1 phosphorylation of Nsk1 antagonizes Nsk1 kinetochore and spindle localization during early mitosis. A nonphosphorylatable Nsk1 mutant binds prematurely to kinetochores and spindle, cementing improper k-MT attachments and leading to high rates of lagging chromosomes that missegregate. Accordingly, cells lacking nsk1 exhibit synthetic growth defects with mutations that disturb MT dynamics and/or kinetochore structure, and lack of proper phosphoregulation leads to even more severe defects. Intriguingly, Nsk1 is stabilized by binding directly to the dynein light chain Dlc1 independently of the dynein motor, and Nsk1-Dlc1 forms chainlike structures in vitro. Our findings establish new roles for Cdk1 and the Nsk1-Dlc1 complex in regulating the k-MT interface and chromosome segregation.
Cdk1 控制有丝分裂染色体行为和纺锤体微管（MT）动力学的许多方面，以确保染色体的准确分离。在本文中，我们描述了裂殖酵母 Cdk1 的一个新的着丝粒底物 Nsk1，它以磷酸化调节的方式促进适当的着丝粒-MT（k-MT）相互作用和染色体运动。Cdk1 对 Nsk1 的磷酸化作用拮抗了早期有丝分裂过程中 Nsk1 着丝粒和纺锤体的定位。一个不可磷酸化的 Nsk1 突变体会过早地与着丝粒和纺锤体结合，固定不正确的 k-MT 连接，导致高比例的滞后染色体错误分离。因此，缺乏 nsk1 的细胞表现出与干扰 MT 动力学和/或着丝粒结构的突变体的合成生长缺陷，而缺乏适当的磷酸化调节会导致更严重的缺陷。有趣的是，Nsk1 通过与独立于动力蛋白的肌球蛋白轻链 Dlc1 直接结合而稳定，并且 Nsk1-Dlc1 在体外形成链状结构。我们的发现为 Cdk1 和 Nsk1-Dlc1 复合物在调节 k-MT 界面和染色体分离方面确立了新的作用。
