Zentrum für Molekulare Biologie, Universität Heidelberg, Heidelberg, Germany.
Cell Cycle. 2011 Oct 1;10(19):3369-78. doi: 10.4161/cc.10.19.17663.
Centromeres are specialized chromatin domains where kinetochores assemble. Centromeres contain as a conserved feature nucleosomes that are composed of the canonical histones H2A, H2B and H4 and a centromere-specific histone H3 variant, known as CENP-A in humans and Cse4 in budding yeast. The incorporation of CENP-A homologues into centromeric chromatin is cell cycle regulated and is assisted by related assembly factors named Scm3 in yeast and HJURP in human cells. Here we describe that the budding yeast Scm3 binds weakly to centromeres during interphase including S phase when Cse4 assembles into centromeres. In anaphase Scm3 then becomes 2.5-fold enriched at kinetochores where it is dynamic with a half recovery time t(1/2) of 36 s. In contrast, Cse4 is stably integrated into kinetochores. In addition, ten Scm3 molecules bind to a cluster of 16 kinetochores with 32 Cse4 molecules suggesting a 1:3 ratio at kinetochores between the two proteins. Analysis of conditional lethal scm3-1 mutant cells indicated that Scm3 participates in maintaining Cse4 at centromeres in anaphase. Thus, Scm3 interacts transiently with kinetochores in anaphase where it safeguards Cse4 even after its S phase incorporation into centromeres.
着丝粒是动粒组装的特化染色质区域。着丝粒包含作为保守特征的核小体，核小体由经典组蛋白 H2A、H2B 和 H4 以及一种着丝粒特异性组蛋白 H3 变体组成，在人类中称为 CENP-A，在芽殖酵母中称为 Cse4。CENP-A 同源物掺入着丝粒染色质是细胞周期调控的，并且受到相关组装因子的辅助，在酵母中称为 Scm3，在人类细胞中称为 HJURP。在这里，我们描述了芽殖酵母 Scm3 在有丝分裂间期（包括 S 期）期间与 Cse4 组装到着丝粒时，与着丝粒的弱结合。在后期，Scm3 在动粒处富集 2.5 倍，在动粒处具有 36 秒的半衰期 t(1/2)。相比之下，Cse4 稳定地整合到动粒中。此外，十个 Scm3 分子结合到一组 16 个动粒，带有 32 个 Cse4 分子，这表明在动粒处两种蛋白质之间的比例为 1:3。对条件致死性 scm3-1 突变细胞的分析表明，Scm3 参与在后期维持 Cse4 在着丝粒处。因此，Scm3 在后期与动粒短暂相互作用，即使在其 S 期掺入到着丝粒后，它也能保护 Cse4。
