Checking fidelity in cell division Everything has to go right during cell division, so a checkpoint mechanism known as the spindle-assembly checkpoint prevents mitosis from proceeding unless the kinetochores that attach chromosomes to the spindle microtubules are properly engaged. Two papers now reveal the detailed molecular choreography that allows a single, unattached kinetochore to arrest cell division: Lara-Gonzalez et al. used a visual probe that tracks a specific form of one of the checkpoint complex proteins, and Piano et al. used a biochemical reconstitution of the checkpoint. Together, these studies reveal how protein interaction, spatial constraints, phosphorylation, and catalytic conversion of the protein Mad2 to its active form allow this all-important sensor to function. Science, this issue p. 64, p. 67 Unattached kinetochores create a signal that protects against chromosome missegregation and aneuploidy. During cell division, kinetochores couple chromosomes to spindle microtubules. To protect against chromosome gain or loss, kinetochores lacking microtubule attachment locally catalyze association of the checkpoint proteins Cdc20 and Mad2, which is the key event in the formation of a diffusible checkpoint complex that prevents mitotic exit. We elucidated the mechanism of kinetochore-catalyzed Mad2-Cdc20 assembly with a probe that specifically monitors this assembly reaction at kinetochores in living cells. We found that catalysis occurs through a tripartite mechanism that includes localized delivery of Mad2 and Cdc20 substrates and two phosphorylation-dependent interactions that geometrically constrain their positions and prime Cdc20 for interaction with Mad2. These results reveal how unattached kinetochores create a signal that ensures genome integrity during cell division.

中文翻译：

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三方机制在独立的动粒处催化 Mad2-Cdc20 组装

检查细胞分裂的保真度 在细胞分裂过程中，一切都必须正确进行，因此称为纺锤体组装检查点的检查点机制会阻止有丝分裂进行，除非将染色体连接到纺锤体微管的动粒正确接合。现在有两篇论文揭示了详细的分子编排，它允许单个独立的动粒阻止细胞分裂：Lara-Gonzalez 等。使用视觉探针跟踪检查点复合蛋白之一的特定形式，而 Piano 等人。使用了检查点的生化重建。总之，这些研究揭示了蛋白质相互作用、空间限制、磷酸化和蛋白质 Mad2 向其活性形式的催化转化是如何使这个非常重要的传感器发挥作用的。科学，这个问题 p。64 页。67 未连接的动粒产生信号，防止染色体错误分离和非整倍性。在细胞分裂过程中，动粒将染色体与纺锤体微管结合。为了防止染色体获得或丢失，缺乏微管附着的动粒局部催化检查点蛋白 Cdc20 和 Mad2 的关联，这是形成可扩散检查点复合物的关键事件，可防止有丝分裂退出。我们用一种探针阐明了动粒催化的 Mad2-Cdc20 组装的机制，该探针专门监测活细胞中动粒的这种组装反应。我们发现催化是通过三方机制发生的，包括 Mad2 和 Cdc20 底物的局部传递和两个依赖磷酸化的相互作用，它们在几何上限制了它们的位置，并为 Cdc20 与 Mad2 相互作用提供了基础。这些结果揭示了未连接的动粒如何产生信号，确保细胞分裂过程中基因组的完整性。