Department of Biochemistry and Molecular Biology, Center for Eukaryotic Gene Regulation, Penn State University, University Park, Pennsylvania, USA.
Mol Cell Biol. 2014 Feb;34(3):303-14. doi: 10.1128/MCB.00478-13. Epub 2013 Nov 18.
Histone N-terminal tails play crucial roles in chromatin-related processes. The tails of histones H3 and H4 are highly conserved and well characterized, but much less is known about the functions of the tails of histones H2A and H2B and their sequences are more divergent among eukaryotes. Here we characterized the function of the only highly conserved region in the H2B tail, the H2B repression (HBR) domain. Once thought to play a role only in repression, it also has an uncharacterized function in gene activation and DNA damage responses. We report that deletion of the HBR domain impairs the eviction of nucleosomes at the promoters and open reading frames of genes. A closer examination of the HBR domain mutants revealed that they displayed phenotypes similar to those of histone chaperone complex FACT mutants, including an increase in intragenic transcription and the accumulation of free histones in cells. Biochemical characterization of recombinant nucleosomes indicates that deletion of the HBR domain impairs FACT-dependent removal of H2A-H2B from nucleosomes, suggesting that the HBR domain plays an important role in allowing FACT to disrupt dimer-DNA interactions. We have uncovered a previously unappreciated role for the HBR domain in regulating chromatin structure and have provided insight into how FACT acts on nucleosomes.
组蛋白 N 端尾部在染色质相关过程中发挥着至关重要的作用。组蛋白 H3 和 H4 的尾部高度保守且特征明显，但组蛋白 H2A 和 H2B 尾部的功能了解较少，并且在真核生物中它们的序列差异更大。在这里，我们研究了 H2B 尾部中唯一高度保守的区域——H2B 抑制（HBR）结构域的功能。该结构域曾被认为仅在抑制中发挥作用，但它在基因激活和 DNA 损伤反应中也具有未被表征的功能。我们报告称，缺失 HBR 结构域会损害启动子和基因开放阅读框处核小体的逐出。对 HBR 结构域突变体的更仔细检查表明，它们表现出与组蛋白伴侣复合物 FACT 突变体相似的表型，包括基因内转录增加和细胞中游离组蛋白的积累。重组核小体的生化特征表明，缺失 HBR 结构域会损害 FACT 依赖性地从核小体中去除 H2A-H2B，表明 HBR 结构域在允许 FACT 破坏二聚体-DNA 相互作用方面发挥着重要作用。我们揭示了 HBR 结构域在调节染色质结构中的先前未被认识的作用，并深入了解了 FACT 如何作用于核小体。
