Crystal structure of the human centromeric nucleosome containing CENP-A

摘要

In eukaryotes, accurate chromosome segregation during mitosis and meiosis is coordinated by kinetochores, which are unique chromosomal sites for microtubule attachment~(1,2). Centromeres specify the kinetochore formation sites on individual chromosomes, and are epigenetically marked by the assembly of nucleo-somes containing the centromere-specific histone H3 variant, CENP-A~(3-12). Although the underlying mechanism is unclear, centromere inheritance is probably dictated by the architecture of the centromeric nucleosome. Here we report the crystal structure of the human centromeric nucleosome containing CENP-A and its cognate a-satellite DNA derivative (147 base pairs). In the human CENP-A nucleosome, the DNA is wrapped around the histone octamer, consisting of two each of histones H2A, H2B, H4 and CENP-A, in a left-handed orientation. However, unlike the canonical H3 nucleosome, only the central 121 base pairs of the DNA are visible. The thirteen base pairs from both ends of the DNA are invisible in the crystal structure, and the aN helix of CENP-A is shorter than that of H3, which is known to be important for the orientation of the DNA ends in the canonical H3 nucleosome13. A structural comparison of the CENP-A and H3 nucleo-somes revealed that CENP-A contains two extra amino acid residues (Arg80 and Gly81) in the loop 1 region, which is completely exposed to the solvent. Mutations of the CENP-A loop 1 residues reduced CENP-A retention at the centromeres in human cells. Therefore, the CENP-A loop 1 may function in stabilizing the centromeric chromatin containing CENP-A, possibly by providing a binding site for trans-acting factors. The structure provides the first atomic-resolution picture of the centromere-specific nucleosome.%“着丝点”是被含有CENP—A(一种着丝点特异rn性组蛋白H3变异体)的核小体组合体通过表观rn遗传方式标记的。Tachiwana等人报告了与rnDNA结合在一起的人“着丝点核小体”的晶体rn结构。他们发现了组蛋白的一个“八聚体”的rn一种标准排列，其中DNA被包裹在一个左手rn向的超级螺旋中。核小体的入口和出口处的rnDNA区域有灵活性，而／CENP-A中的一个回环rn则可帮助稳定其向“着丝点染色质”中的融合。rn作为含CENP-A的核小体的第一个已知结构，rn它可帮助澄清在文献中一直被争论的各种不rn同模型。