The activity of the histone chaperone yeast Asf1 in the assembly and disassembly of histone H3/H4-DNA complexes.
The activity of the histone chaperone yeast Asf1 in the assembly and disassembly of histone H3/H4-DNA complexes.
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DOI：
10.1093/nar/gkr097
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发表时间：
2011-07
影响因子：
14.9
通讯作者：
Churchill ME
中科院分区：
文献类型：
--
作者：
Donham DC 2nd;Scorgie JK;Churchill ME
组蛋白H3/H4沉积在DNA上形成四体中间体，H3/H4从DNA上移位是核小体组装和拆解的第一步和最后一步。抗沉默功能1(ASF1)是H3/H4二聚体的伴侣，在这两个过程中都发挥作用。然而，人们对伴侣蛋白-组蛋白相互作用的热力学或ASF1在组蛋白-DNA复合体的形成或拆解中的直接作用知之甚少。在这里，我们发现酿酒酵母ASF1保护H3/H4免受不利的DNA相互作用，并通过二体的形成帮助形成有利的组蛋白-DNA相互作用。然而，对于由H3/H4和强核小体定位DNA序列形成的四体或被突变的(H3K56Q/H4)组蛋白或非定位DNA序列削弱的四体，ASF1不能使组蛋白从DNA上解离。此外，ASF1不与预先形成的四体相关联。这些结果与ASF1对2.5DNA的H3/H4二聚体的亲和力测定是一致的，这一亲和力弱于H3/H4对 的结合。这些研究支持ASF1帮助H3/H4沉积到DNA上的机制，但表明ASF1需要额外的因子或翻译后修饰才能从染色质的四体中间体中去除H3/H4。
The deposition of the histones H3/H4 onto DNA to give the tetrasome intermediate and the displacement of H3/H4 from DNA are thought to be the first and the last steps in nucleosome assembly and disassembly, respectively. Anti-silencing function 1 (Asf1) is a chaperone of the H3/H4 dimer that functions in both of these processes. However, little is known about the thermodynamics of chaperone–histone interactions or the direct role of Asf1 in the formation or disassembly of histone–DNA complexes. Here, we show that Saccharomyces cerevisiae Asf1 shields H3/H4 from unfavorable DNA interactions and aids the formation of favorable histone–DNA interactions through the formation of disomes. However, Asf1 was unable to disengage histones from DNA for tetrasomes formed with H3/H4 and strong nucleosome positioning DNA sequences or tetrasomes weakened by mutant (H3K56Q/H4) histones or non-positioning DNA sequences. Furthermore, Asf1 did not associate with preformed tetrasomes. These results are consistent with the measured affinity of Asf1 for H3/H4 dimers of 2.5 nM, which is weaker than the association of H3/H4 for DNA. These studies support a mechanism by which Asf1 aids H3/H4 deposition onto DNA but suggest that additional factors or post-translational modifications are required for Asf1 to remove H3/H4 from tetrasome intermediates in chromatin.
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