Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, USA.
Nucleic Acids Res. 2021 May 7;49(8):4750-4767. doi: 10.1093/nar/gkab246.
Hexasomes and tetrasomes are intermediates in nucleosome assembly and disassembly. Their formation is promoted by histone chaperones, ATP-dependent remodelers, and RNA polymerase II. In addition, hexasomes are maintained in transcribed genes and could be an important regulatory factor. While nucleosome composition has been shown to affect the structure and accessibility of DNA, its influence on histone tails is largely unknown. Here, we investigate the conformational dynamics of the H3 tail in the hexasome and tetrasome. Using a combination of NMR spectroscopy, MD simulations, and trypsin proteolysis, we find that the conformational ensemble of the H3 tail is regulated by nucleosome composition. As has been found for the nucleosome, the H3 tails bind robustly to DNA within the hexasome and tetrasome, but upon loss of the H2A/H2B dimer, we determined that the adjacent H3 tail has an altered conformational ensemble, increase in dynamics, and increase in accessibility. Similar to observations of DNA dynamics, this is seen to be asymmetric in the hexasome. Our results indicate that nucleosome composition has the potential to regulate chromatin signaling and ultimately help shape the chromatin landscape.
六聚体和四聚体是核小体组装和拆卸的中间产物。它们的形成受组蛋白伴侣、ATP 依赖性重塑酶和 RNA 聚合酶 II 的促进。此外，六聚体在转录基因中得以维持，可能是一个重要的调节因子。虽然核小体组成已被证明会影响 DNA 的结构和可及性，但它对组蛋白尾部的影响在很大程度上仍是未知的。在这里，我们研究了六聚体和四聚体中 H3 尾部的构象动力学。我们使用 NMR 光谱、MD 模拟和胰蛋白酶水解的组合，发现 H3 尾部的构象整体由核小体组成所调节。与核小体一样，H3 尾部在六聚体和四聚体中与 DNA 结合牢固，但当失去 H2A/H2B 二聚体时，我们确定相邻的 H3 尾部具有改变的构象整体，增加了动力学，并增加了可及性。与观察到的 DNA 动力学类似，这种现象在六聚体中是不对称的。我们的结果表明，核小体组成有可能调节染色质信号转导，并最终有助于塑造染色质景观。
