Histone H3 variants specify modes of chromatin assembly
Histone H3 variants specify modes of chromatin assembly
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DOI：
10.1073/pnas.172403699
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发表时间：
2002-12-10
影响因子：
11.1
通讯作者：
Henikoff, S
中科院分区：
文献类型：
--
作者：
Ahmad, K;Henikoff, S
组蛋白变体已被发现30年，但其功能以及它们沉积的机制在很大程度上仍然未知。果蝇有三种组蛋白H3。H3包裹大部分基因组，H3.3标记活性染色质，可能对基因调控至关重要，而Cid是着丝粒染色质的特征性结构成分。我们利用一个果蝇细胞系系统对这些组蛋白的特性进行了表征，该系统可对DNA复制和组蛋白沉积进行精确分析。H3的沉积仅限于复制的DNA。与之形成鲜明对比的是，H3.3和Cid在整个细胞周期中都可沉积。H3.3的沉积不伴随任何相应的DNA复制。为了证实Cid的沉积也是不依赖复制的（RI），我们检测了培养细胞和神经母细胞中的着丝粒复制。我们发现着丝粒与异染色质不同步复制，并显示出可能限制H3沉积的复制模式。这证实了这两种变体都经历不依赖复制的沉积，但在细胞核的不同位置。变体组蛋白如何实现不依赖复制的沉积尚不清楚，这引发了关于核小体稳定性、完成核小体组装的机制以及细胞核功能组织的基本问题。H3、H3.3和Cid在体内的不同特性为确定它们被差异靶向的机制奠定了基础。在此我们提出，“开放”染色质的局部效应以及核组织的更广泛效应有助于引导两种不同的H3变体到达其靶位点。
Histone variants have been known for 30 years, but their functions and the mechanism of their deposition are still largely unknown. Drosophila has three versions of histone H3. H3 packages the bulk genome, H3.3 marks active chromatin and may be essential for gene regulation, and Cid is the characteristic structural component of centromeric chromatin. We have characterized the properties of these histones by using a Drosophila cell-line system that allows precise analysis of both DNA replication and histone deposition. The deposition of H3 is restricted to replicating DNA. In striking contrast, H3.3 and Cid deposit throughout the cell cycle. Deposition of H3.3 occurs without any corresponding DNA replication. To confirm that the deposition of Cid is also replication-independent (RI), we examined centromere replication in cultured cells and neuroblasts. We found that centromeres replicate out of phase with heterochromatin and display replication patterns that may limit H3 deposition. This confirms that both variants undergo RI deposition, but at different locations in the nucleus. How variant histones accomplish RI deposition is unknown, and raises basic questions about the stability of nucleosomes, the machinery that accomplishes nucleosome assembly, and the functional organization of the nucleus. The different in vivo properties of H3, H3.3, and Cid set the stage for identifying the mechanisms by which they are differentially targeted. Here we suggest that local effects of "open" chromatin and broader effects of nuclear organization help to guide the two different H3 variants to their target sites.