Department of Biochemistry, Stanford Medical School, Beckman 409A, Stanford, California 94305-5307, USA.
Nature. 2011 Aug 28;477(7364):354-8. doi: 10.1038/nature10379.
During cell division, chromosomes are segregated to nascent daughter cells by attaching to the microtubules of the mitotic spindle through the kinetochore. Kinetochores are assembled on a specialized chromatin domain called the centromere, which is characterized by the replacement of nucleosomal histone H3 with the histone H3 variant centromere protein A (CENP-A). CENP-A is essential for centromere and kinetochore formation in all eukaryotes but it is unknown how CENP-A chromatin directs centromere and kinetochore assembly. Here we generate synthetic CENP-A chromatin that recapitulates essential steps of centromere and kinetochore assembly in vitro. We show that reconstituted CENP-A chromatin when added to cell-free extracts is sufficient for the assembly of centromere and kinetochore proteins, microtubule binding and stabilization, and mitotic checkpoint function. Using chromatin assembled from histone H3/CENP-A chimaeras, we demonstrate that the conserved carboxy terminus of CENP-A is necessary and sufficient for centromere and kinetochore protein recruitment and function but that the CENP-A targeting domain--required for new CENP-A histone assembly--is not. These data show that two of the primary requirements for accurate chromosome segregation, the assembly of the kinetochore and the propagation of CENP-A chromatin, are specified by different elements in the CENP-A histone. Our unique cell-free system enables complete control and manipulation of the chromatin substrate and thus presents a powerful tool to study centromere and kinetochore assembly.
在细胞分裂过程中,染色体通过附着在有丝分裂纺锤体的微管上来分离到新形成的子细胞中,这种附着是通过动粒实现的。动粒组装在一个称为着丝粒的特殊染色质域上,其特征是用组蛋白 H3 变体着丝粒蛋白 A(CENP-A)取代核小体组蛋白 H3。CENP-A 对于所有真核生物的着丝粒和动粒的形成都是必不可少的,但尚不清楚 CENP-A 染色质如何指导着丝粒和动粒的组装。在这里,我们生成了模拟 CENP-A 染色质的人工制品,该制品在体外重现了着丝粒和动粒组装的基本步骤。我们表明,当添加到无细胞提取物中时,重新构成的 CENP-A 染色质足以组装着丝粒和动粒蛋白、微管结合和稳定以及有丝分裂检查点功能。使用组蛋白 H3/CENP-A 嵌合体组装的染色质,我们证明 CENP-A 的保守羧基末端对于招募和功能的着丝粒和动粒蛋白是必需和充分的,但对于新 CENP-A 组蛋白组装所必需的 CENP-A 靶向结构域不是必需的。这些数据表明,准确的染色体分离的两个主要要求,即动粒的组装和 CENP-A 染色质的传播,是由 CENP-A 组蛋白中的不同元件指定的。我们独特的无细胞系统能够完全控制和操作染色质底物,因此为研究着丝粒和动粒的组装提供了一个强大的工具。