Nucleosome-depleted chromatin gaps recruit assembly factors for the H3.3 histone variant
Nucleosome-depleted chromatin gaps recruit assembly factors for the H3.3 histone variant
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DOI：
10.1073/pnas.1206629109
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发表时间：
2012-11-27
影响因子：
11.1
通讯作者：
Ahmad, Kami
中科院分区：
文献类型：
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作者：
Schneiderman, Jonathan I.;Orsi, Guillermo A.;Ahmad, Kami
包装真核生物DNA的大多数核小体在DNA复制期间组装，但染色质结构在基因组的活性区域中通常被破坏。使用H3.3组蛋白变体的不依赖复制的核小体替换有效地重新包装这些区域，但是组蛋白如何被募集到这些位点尚不清楚。在这里，我们使用一个诱导系统，产生核小体耗尽的染色质在果蝇的热休克蛋白70基因，以确定核小体替换机制的步骤。我们发现，Xnp染色质重塑和希拉组蛋白伴侣独立绑定核小体耗尽染色质。令人惊讶的是，这两个因子只有在新的核小体组装时才被取代。H3.3沉积试验表明，Xnp和Hira是有效的核小体置换所必需的，双突变体是致命的。我们建议Xnp和Hira识别暴露的DNA，并作为一个有效的招聘H3.3预沉积复合物染色质间隙的结合平台。这些结果揭示了真核细胞主动防止细胞核中DNA暴露的机制。
Most nucleosomes that package eukaryotic DNA are assembled during DNA replication, but chromatin structure is routinely disrupted in active regions of the genome. Replication-independent nucleosome replacement using the H3.3 histone variant efficiently repackages these regions, but how histones are recruited to these sites is unknown. Here, we use an inducible system that produces nucleosome-depleted chromatin at the Hsp70 genes in Drosophila to define steps in the mechanism of nucleosome replacement. We find that the Xnp chromatin remodeler and the Hira histone chaperone independently bind nucleosome-depleted chromatin. Surprisingly, these two factors are only displaced when new nucleosomes are assembled. H3.3 deposition assays reveal that Xnp and Hira are required for efficient nucleosome replacement, and double-mutants are lethal. We propose that Xnp and Hira recognize exposed DNA and serve as a binding platform for the efficient recruitment of H3.3 predeposition complexes to chromatin gaps. These results uncover the mechanisms by which eukaryotic cells actively prevent the exposure of DNA in the nucleus.