Sir3-Nucleosome Interactions in Spreading of Silent Chromatin in Saccharomyces cerevisiae
Sir3-Nucleosome Interactions in Spreading of Silent Chromatin in Saccharomyces cerevisiae
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DOI：
10.1128/mcb.01210-08
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发表时间：
2008-11-15
影响因子：
5.3
通讯作者：
Moazed, Danesh
中科院分区：
文献类型：
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作者：
Buchberger, Johannes R.;Onishi, Megumi;Moazed, Danesh
酿酒酵母中的沉默染色质是通过涉及 SIR 复合物的逐步过程建立的，该复合物由组蛋白脱乙酰酶 Sir2 以及结构成分 Sir3 和 Sir4 组成。 Sir3 蛋白是 SIR 复合物的主要组蛋白结合成分，在体外形成寡聚物，并被认为介导 SIR 复合物沿染色质纤维的扩散。为了分析 Sir3 在 SIR 复合物传播中的作用，我们对显性破坏沉默的 SIR3 等位基因进行了有针对性的遗传筛选。大多数突变映射到保守的 N 端 BAH 结构域中的单个表面，而一种突变 L738P 定位于 Sir3 C 端半部内的 AAA ATP 酶样结构域。 BAH 点突变体（而非 L738P 突变体）破坏了 Sir3 和核小体之间的相互作用。相比之下，Sir3-L738P 与组蛋白 H4 N 端尾部的结合比野生型 Sir3 更强，表明 Sir3 C 端组蛋白结合活性的错误调节也会破坏扩散。我们的结果强调了 Sir3 和核小体之间在沉默染色质组装中适当相互作用的重要性。我们提出了一个 SIR 复合物通过 Sir3 中两个不同的组蛋白结合域沿着染色质纤维扩散的模型。
Silent chromatin in Saccharomyces cerevisiae is established in a stepwise process involving the SIR complex, comprised of the histone deacetylase Sir2 and the structural components Sir3 and Sir4. The Sir3 protein, which is the primary histone-binding component of the SIR complex, forms oligomers in vitro and has been proposed to mediate the spreading of the SIR complex along the chromatin fiber. In order to analyze the role of Sir3 in the spreading of the SIR complex, we performed a targeted genetic screen for alleles of SIR3 that dominantly disrupt silencing. Most mutations mapped to a single surface in the conserved N-terminal BAH domain, while one, L738P, localized to the AAA ATPase-like domain within the C-terminal half of Sir3. The BAH point mutants, but not the L738P mutant, disrupted the interaction between Sir3 and nucleosomes. In contrast, Sir3-L738P bound the N-terminal tail of histone H4 more strongly than wild-type Sir3, indicating that misregulation of the Sir3 C-terminal histone-binding activity also disrupted spreading. Our results underscore the importance of proper interactions between Sir3 and the nucleosome in silent chromatin assembly. We propose a model for the spreading of the SIR complex along the chromatin fiber through the two distinct histone-binding domains in Sir3.