Wellcome Trust Centre for Gene Regulation and Expression, Nucleic Acid Structure Research Group, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
Nucleic Acids Res. 2010 Jan;38(2):695-707. doi: 10.1093/nar/gkp1003. Epub 2009 Nov 13.
The (H3-H4)(2) histone tetramer forms the central core of nucleosomes and, as such, plays a prominent role in assembly, disassembly and positioning of nucleosomes. Despite its fundamental role in chromatin, the tetramer has received little structural investigation. Here, through the use of pulsed electron-electron double resonance spectroscopy coupled with site-directed spin labelling, we survey the structure of the tetramer in solution. We find that tetramer is structurally more heterogeneous on its own than when sequestered in the octamer or nucleosome. In particular, while the central region including the H3-H3' interface retains a structure similar to that observed in nucleosomes, other regions such as the H3 alphaN helix display increased structural heterogeneity. Flexibility of the H3 alphaN helix in the free tetramer also illustrates the potential for post-translational modifications to alter the structure of this region and mediate interactions with histone chaperones. The approach described here promises to prove a powerful system for investigating the structure of additional assemblies of histones with other important factors in chromatin assembly/fluidity.
（H3-H4）（2）组蛋白四聚体构成核小体的核心，因此在核小体的组装、拆卸和定位中发挥着重要作用。尽管它在染色质中起着基本作用，但四聚体的结构研究却很少。在这里，我们通过使用脉冲电子-电子双共振光谱结合定点自旋标记，在溶液中研究了四聚体的结构。我们发现，四聚体本身的结构比封闭在八聚体或核小体中时更具异质性。特别是，虽然包括 H3-H3' 界面在内的中心区域保留了与核小体中观察到的相似的结构，但其他区域，如 H3αN 螺旋，显示出更高的结构异质性。在游离四聚体中 H3αN 螺旋的柔韧性也说明了翻译后修饰可能改变该区域的结构并介导与组蛋白伴侣的相互作用。这里描述的方法有望成为研究与染色质组装/流动性相关的其他组蛋白和其他重要因素的组装体结构的强大系统。
