Weber Stewart A, Gerton Jennifer L, Polancic Joan E, DeRisi Joseph L, Koshland Douglas, Megee Paul C
Department of Biochemistry and Molecular Genetics, University of Colorado Health Sciences Center at Fitzsimons, Aurora, Colorado, USA.
PLoS Biol. 2004 Sep;2(9):E260. doi: 10.1371/journal.pbio.0020260. Epub 2004 Jul 27.
The recruitment of cohesins to pericentric chromatin in some organisms appears to require heterochromatin associated with repetitive DNA. However, neocentromeres and budding yeast centromeres lack flanking repetitive DNA, indicating that cohesin recruitment occurs through an alternative pathway. Here, we demonstrate that all budding yeast chromosomes assemble cohesin domains that extend over 20-50 kb of unique pericentric sequences flanking the conserved 120-bp centromeric DNA. The assembly of these cohesin domains requires the presence of a functional kinetochore in every cell cycle. A similar enhancement of cohesin binding was also observed in regions flanking an ectopic centromere. At both endogenous and ectopic locations, the centromeric enhancer amplified the inherent levels of cohesin binding that are unique to each region. Thus, kinetochores are enhancers of cohesin association that act over tens of kilobases to assemble pericentric cohesin domains. These domains are larger than the pericentric regions stretched by microtubule attachments, and thus are likely to counter microtubule-dependent forces. Kinetochores mediate two essential segregation functions: chromosome movement through microtubule attachment and biorientation of sister chromatids through the recruitment of high levels of cohesin to pericentric regions. We suggest that the coordination of chromosome movement and biorientation makes the kinetochore an autonomous segregation unit.
在某些生物体中,黏连蛋白募集到着丝粒周围染色质似乎需要与重复DNA相关的异染色质。然而,新着丝粒和芽殖酵母着丝粒缺乏侧翼重复DNA,这表明黏连蛋白的募集是通过一条替代途径发生的。在这里,我们证明所有芽殖酵母染色体都会组装黏连蛋白结构域,这些结构域延伸超过保守的120bp着丝粒DNA侧翼20 - 50kb的独特着丝粒周围序列。这些黏连蛋白结构域的组装在每个细胞周期都需要有功能的动粒存在。在异位着丝粒侧翼区域也观察到了类似的黏连蛋白结合增强现象。在内源和异位位置,着丝粒增强子都放大了每个区域特有的黏连蛋白结合固有水平。因此,动粒是黏连蛋白结合的增强子,作用于数十千碱基以组装着丝粒周围黏连蛋白结构域。这些结构域比微管附着拉伸的着丝粒周围区域更大,因此可能对抗微管依赖性力。动粒介导两种基本的分离功能:通过微管附着进行染色体移动以及通过将高水平的黏连蛋白募集到着丝粒周围区域实现姐妹染色单体的双定向。我们认为染色体移动和双定向的协调使动粒成为一个自主的分离单元。