Furuyama Suzanne, Biggins Sue
Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, PO Box 19024, Seattle, WA 98109, USA.
Proc Natl Acad Sci U S A. 2007 Sep 11;104(37):14706-11. doi: 10.1073/pnas.0706985104. Epub 2007 Sep 5.
Chromosome segregation ensures that DNA is equally divided between daughter cells during each round of cell division. The centromere (CEN) is the specific locus on each chromosome that directs formation of the kinetochore, the multiprotein complex that interacts with the spindle microtubules to promote proper chromosomal alignment and segregation during mitosis. CENs are organized into a specialized chromatin structure due to the incorporation of an essential CEN-specific histone H3 variant (CenH3) in the centromeric nucleosomes of all eukaryotes. Consistent with its essential role at the CEN, the loss or up-regulation of CenH3 results in mitotic defects. Despite the requirement for CenH3 in CEN function, it is unclear how CenH3 nucleosomes structurally organize centromeric DNA to promote formation of the kinetochore. To address this issue, we developed a modified chromatin immunoprecipitation approach to analyze the number and position of CenH3 nucleosomes at the budding yeast CEN. Using this technique, we show that yeast CENs have a single CenH3 nucleosome positioned over the CEN-determining elements. Therefore, a single CenH3 nucleosome forms the minimal unit of centromeric chromatin necessary for kinetochore assembly and proper chromosome segregation.
染色体分离确保在每一轮细胞分裂过程中，DNA能在子细胞间平均分配。着丝粒（CEN）是每条染色体上的特定位点，它指导动粒的形成，动粒是一种多蛋白复合体，在有丝分裂期间与纺锤体微管相互作用，以促进染色体正确排列和分离。由于在所有真核生物的着丝粒核小体中都掺入了一种必需的着丝粒特异性组蛋白H3变体（CenH3），着丝粒被组织成一种特殊的染色质结构。与其在着丝粒的关键作用一致，CenH3的缺失或上调会导致有丝分裂缺陷。尽管CenH3在着丝粒功能中是必需的，但尚不清楚CenH3核小体如何在结构上组织着丝粒DNA以促进动粒的形成。为了解决这个问题，我们开发了一种改良的染色质免疫沉淀方法，以分析芽殖酵母着丝粒处CenH3核小体的数量和位置。使用这项技术，我们表明酵母着丝粒有一个位于着丝粒决定元件上的单一CenH3核小体。因此，单个CenH3核小体形成了动粒组装和正确染色体分离所需的着丝粒染色质的最小单位。
