Department of Biochemistry, Stanford University Medical School, Stanford, CA 94305, USA.
J Cell Biol. 2011 Sep 19;194(6):855-71. doi: 10.1083/jcb.201106079. Epub 2011 Sep 12.
Eukaryotic chromosomes segregate by attaching to microtubules of the mitotic spindle through a chromosomal microtubule binding site called the kinetochore. Kinetochores assemble on a specialized chromosomal locus termed the centromere, which is characterized by the replacement of histone H3 in centromeric nucleosomes with the essential histone H3 variant CENP-A (centromere protein A). Understanding how CENP-A chromatin is assembled and maintained is central to understanding chromosome segregation mechanisms. CENP-A nucleosome assembly requires the Mis18 complex and the CENP-A chaperone HJURP. These factors localize to centromeres in telophase/G1, when new CENP-A chromatin is assembled. The mechanisms that control their targeting are unknown. In this paper, we identify a mechanism for recruiting the Mis18 complex protein M18BP1 to centromeres. We show that depletion of CENP-C prevents M18BP1 targeting to metaphase centromeres and inhibits CENP-A chromatin assembly. We find that M18BP1 directly binds CENP-C through conserved domains in the CENP-C protein. Thus, CENP-C provides a link between existing CENP-A chromatin and the proteins required for new CENP-A nucleosome assembly.
真核染色体通过附着在有丝分裂纺锤体的微管上来进行分离，这种附着是通过一个叫做动粒的染色体微管结合位点实现的。动粒组装在一个被称为着丝粒的特殊染色体位点上，着丝粒的特征是用必需的组蛋白 H3 变体 CENP-A（着丝粒蛋白 A）取代着丝粒核小体中的组蛋白 H3。了解 CENP-A 染色质是如何组装和维持的，对于理解染色体分离机制至关重要。CENP-A 核小体的组装需要 Mis18 复合物和 CENP-A 伴侣蛋白 HJURP。这些因子在末期/ G1 时定位于着丝粒，此时会组装新的 CENP-A 染色质。控制它们靶向的机制尚不清楚。在本文中，我们确定了一种将 Mis18 复合物蛋白 M18BP1 募集到着丝粒的机制。我们表明，CENP-C 的耗竭会阻止 M18BP1 靶向中期着丝粒，并抑制 CENP-A 染色质的组装。我们发现 M18BP1 通过 CENP-C 蛋白中的保守结构域直接与 CENP-C 结合。因此，CENP-C 为现有 CENP-A 染色质和组装新的 CENP-A 核小体所需的蛋白质之间提供了联系。
