Ludwig Institute for Cancer Research and Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92037, USA.
J Cell Biol. 2012 Feb 20;196(4):469-82. doi: 10.1083/jcb.201111107. Epub 2012 Feb 13.
Accurate chromosome segregation requires coordination between microtubule attachment and spindle checkpoint signaling at the kinetochore. The kinetochore-localized KMN (KNL-1/Mis12 complex/Ndc80 complex) network, which mediates microtubule attachment and scaffolds checkpoint signaling, harbors two distinct microtubule-binding activities: the load-bearing activity of the Ndc80 complex and a less well-understood activity in KNL-1. In this paper, we show that KNL-1 microtubule-binding and -bundling activity resides in its extreme N terminus. Selective perturbation of KNL-1 microtubule binding in Caenorhabditis elegans embryos revealed that this activity is dispensable for both load-bearing attachment formation and checkpoint activation but plays a role in checkpoint silencing at the kinetochore. Perturbation of both microtubule binding and protein phosphatase 1 docking at the KNL-1 N terminus additively affected checkpoint silencing, indicating that, despite their proximity in KNL-1, these two activities make independent contributions. We propose that microtubule binding by KNL-1 functions in checkpoint silencing by sensing microtubules attached to kinetochores and relaying their presence to eliminate generation of the checkpoint signal.
准确的染色体分离需要动粒处微管附着与纺锤体检验点信号之间的协调。动粒定位的 KMN（KNL-1/Mis12 复合物/Ndc80 复合物）网络介导微管附着并作为检验点信号的支架，它拥有两种不同的微管结合活性：Ndc80 复合物的承载活性和 KNL-1 中一种理解较少的活性。在本文中，我们表明 KNL-1 的微管结合和束状活性位于其极端的 N 端。在秀丽隐杆线虫胚胎中选择性地干扰 KNL-1 的微管结合，揭示了该活性对于承载附着的形成和检验点的激活都是可有可无的，但在动粒处的检验点沉默中发挥作用。在 KNL-1 的 N 端同时干扰微管结合和蛋白磷酸酶 1 对接，会附加地影响检验点沉默，表明尽管在 KNL-1 中它们很接近，但这两种活性具有独立的作用。我们提出，KNL-1 的微管结合通过感知附着在动粒上的微管并将其存在传递出去以消除检验点信号的产生，从而在检验点沉默中发挥作用。
