Nurse Nathan P, Yuan Chongli
School of Chemical Engineering, Purdue University, West Lafayette, IN, 47906.
Biopolymers. 2015 Jan;103(1):33-40. doi: 10.1002/bip.22560.
Chromatin structure and the transcriptional state of a gene can be modulated by modifications made on H3 and H4 tails of histones. Elucidating the internucleosomal interactions of these tails is vital to understanding epigenetic regulation. Differentiation between cis (intra-nucleosomal) and trans (inter-nucleosomal) interactions is often difficult with conventional techniques since H3 and H4 tails are flexible. The distinction, however, is important because these interactions model short- and long-range chromatin interactions respectively and have different bearings in biological processes. Combining FCS and PCH analysis, we can decouple the contribution of histone tails to cis and trans effects. A Mg(2+) gradient was employed to facilitate compaction and oligomerization of tetranucleosomes with H3 and/or H4 tail truncations. H3 tails were found to play a multifunctional role and exhibit the ability to partake in both attractive cis and trans interactions simultaneously. H4 tails partake in attractive cis and repulsive trans interactions at low [Mg(2+)]. These interactions are diminished at higher [Mg(2+)]. Simultaneous H3 and H4 tail truncation inhibited array oligomerization but maintained local array compaction at relatively high [Mg(2+)]. The established experimental approach can be extended to study the detailed molecular interactions mediated by epigenetic modification of flexible histone tails.
染色质结构和基因的转录状态可通过组蛋白H3和H4尾巴上的修饰来调节。阐明这些尾巴的核小体间相互作用对于理解表观遗传调控至关重要。由于H3和H4尾巴具有灵活性，使用传统技术区分顺式（核小体内）和反式（核小体间）相互作用往往很困难。然而，这种区分很重要，因为这些相互作用分别模拟了短程和长程染色质相互作用，并且在生物过程中具有不同的影响。结合荧光相关光谱（FCS）和光子相关光谱（PCH）分析，我们可以分离组蛋白尾巴对顺式和反式效应的贡献。采用镁离子（Mg(2+)）梯度来促进具有H3和/或H4尾巴截短的四核小体的压缩和寡聚化。发现H3尾巴发挥多功能作用，并表现出同时参与有吸引力的顺式和反式相互作用的能力。在低Mg(2+)浓度下，H4尾巴参与有吸引力的顺式和排斥性的反式相互作用。在较高的Mg(2+)浓度下，这些相互作用会减弱。同时截短H3和H4尾巴会抑制阵列寡聚化，但在相对较高的Mg(2+)浓度下保持局部阵列压缩。已建立的实验方法可扩展用于研究由灵活的组蛋白尾巴的表观遗传修饰介导的详细分子相互作用。
