Histones in transit: Cytosolic histone complexes and diacetylation of H4 during nucleosome assembly in human cells
Histones in transit: Cytosolic histone complexes and diacetylation of H4 during nucleosome assembly in human cells
复制标题
DOI：
10.1021/bi962069i
复制
发表时间：
1997-01-21
期刊：
影响因子：
2.9
通讯作者：
Annunziato, AT
中科院分区：
文献类型：
--
作者：
Chang, L;Loranger, SS;Annunziato, AT
检查新生组蛋白在稳定掺入染色质之前的组织和乙酰化。通过对 HeLa 胞质提取物进行沉降和免疫沉淀分析，检测到两种体细胞非核小体组蛋白复合物：一种含有新生的 H3 和 H4，另一种含有与非组蛋白 NAP-1 相关的 H2A（也可能是 H2B）。 H3/H4 复合物的沉降系数为 5-6S，与一种或多种护航蛋白的存在一致。胞质H3/H4复合物中的H4被双乙酰化，与染色质中新合成的H4的乙酰化状态完全一致。因此，新生人类 H4 的二乙酰化在核小体组装之前完成。作为我们对新生 H3/H4 复合物研究的一部分，还研究了最有可能负责乙酰化新合成的 H4 的细胞质组蛋白乙酰转移酶。 HeLa 组蛋白乙酰转移酶 B (HAAT B) 在体外乙酰化 H4 但不乙酰化 H3，即使在丁酸钠存在下也能最大程度地二乙酰化 H4。人 HAT B 仅在位置 5 和 12 的赖氨酸残基上乙酰化 H4，与新生核小体 H4 的高度保守的乙酰化模式完全一致（Sobel 等人，1995），并且具有类似于 100 kDa 的天然分子量。基于我们的发现，提出了一个模型，用于说明组蛋白乙酰化和 NAP-1 在体内核小体组装和染色质重塑过程中参与 H2A/H2B 沉积和交换。
The organization and acetylation of nascent histones prior to their stable incorporation into chromatin were examined. Through sedimentation and immunoprecipitation analyses of HeLa cytosolic extracts, two somatic non-nucleosomal histone complexes were detected: one containing nascent H3 and H4, and a second containing H2A (and probably H2B) in association with the nonhistone protein NAP-1. The H3/H4 complex has a sedimentation coefficient of 5-6S, consistent with the presence of one or more escort proteins. H4 in the cytosolic H3/H4 complex is diacetylated, fully in accord with the acetylation state of newly synthesized H4 in chromatin. The diacetylation of nascent human H4 is therefore completed prior to nucleosome assembly. As part of our studies of the nascent H3/H4 complex, the cytoplasmic histone acetyltransferase most likely responsible for acetylating newly synthesized H4 was also investigated. HeLa histone acetyltransferase B (HAT B) acetylates H4 but not H3 in vitro, and maximally diacetylates H4 even in the presence of sodium butyrate. Human HAT B acetylates H4 exclusively on the lysine residues at positions 5 and 12, in complete agreement with the highly conserved acetylation pattern of nascent nucleosomal H4 (Sobel et al., 1995), and has a native molecular weight of similar to 100 kDa. Based on our findings a model is presented for the involvement of histone acetylation and NAP-1 in H2A/H2B deposition and exchange, during nucleosome assembly and chromatin remodeling in vivo.