Targeting of cohesin by transcriptionally silent chromatin
Targeting of cohesin by transcriptionally silent chromatin
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DOI：
10.1101/gad.1356305
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发表时间：
2005-12-15
影响因子：
10.5
通讯作者：
Gartenberg, MR
中科院分区：
文献类型：
--
作者：
Chang, CR;Wu, CS;Gartenberg, MR
真核DNA复制产生姐妹染色单体，这些姐妹染色单体通过粘着蛋白连接在一起，直到分裂后期，粘着蛋白是一种环形蛋白质复合物，被认为通过拥抱两个染色单体起作用。粘着蛋白富集在着丝粒，以及沿着染色体臂的离散位点，其中转录将复合物定位在会聚基因对之间。粘连蛋白和sir介导的转录沉默之间的关系也开始出现。在这里，我们使用荧光显微镜和位点特异性重组来表征沉默HMR交配型基因座的新复制副本之间的相互作用。HMR用lac-GFP标记，并且侧翼为可诱导的位点特异性重组酶的结合位点。在具有姐妹染色单体的细胞中切除该位点产生了两个染色质环，它们彼此保持关联。圆圈的配对需要沉默的染色质、粘着蛋白和RSC染色质重塑复合物。染色质免疫沉淀表明，靶向的cohesin的位点是sir依赖性的，和功能测试表明，沉默的染色质的行为在一个连续的方式，以保持凝聚力。值得注意的是，沉默的丧失导致内聚蛋白的丧失。来自线性染色体模板，但不是来自切除的染色质环。结果是一致的模型，其中黏结蛋白结合沉默染色质通过拓扑连接到个别染色单体。
Eukaryotic DNA replication produces sister chromatids that are linked together until anaphase by cohesin, a ring-shaped protein complex that is thought to act by embracing both chromatids. Cohesin is enriched at centromeres, as well as discrete sites along chromosome arms where transcription positions the complex between convergent gene pairs. A relationship between cohesin and Sir-mediated transcriptional silencing has also begun to emerge. Here we used fluorescence microscopy and site-specific recombination to characterize interactions between newly replicated copies of the silent HMR mating-type locus. HMR was tagged with lac-GFP and flanked by binding sites for an inducible site-specific recombinase. Excision of the locus in cells with sister chromatids produced two chromatin circles that remained associated with one another. Pairing of the circles required silent chromatin, cohesin, and the RSC chromatin-remodeling complex. Chromatin immunoprecipitation showed that targeting of cohesin to the locus is Sir-dependent, and functional tests showed that silent chromatin acts in a continuous fashion to maintain cohesion. Remarkably, loss of silencing led to loss of cohesiin. from linear chromosomal templates but not from excised chromatin circles. The results are consistent with a model in which cohesin binds silent chromatin via topological linkage to individual chromatids.