Structural Analysis of the Hexasome, Lacking One Histone H2A/H2B Dimer from the Conventional Nucleosome
Structural Analysis of the Hexasome, Lacking One Histone H2A/H2B Dimer from the Conventional Nucleosome
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DOI：
10.1021/bi300129b
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发表时间：
2012-04-17
期刊：
影响因子：
2.9
通讯作者：
Kurumizaka, Hitoshi
中科院分区：
文献类型：
--
作者：
Arimura, Yasuhiro;Tachiwana, Hiroaki;Kurumizaka, Hitoshi
在真核生物中，基因组DNA被包装在染色质中，核小体是染色质的基本单位。典型的核小体是八体，其由两个H2 A/H2 B二聚体和两个H3/H4二聚体组成。在转录延伸过程中，H2 A/H2 B二聚体之一从八体中移除。H2 A/H2 B二聚体的消耗也被认为发生在DNA复制和修复过程中。其余的组蛋白组分被认为维持称为“六酶体”的核小体结构，其可能对于基因表达、DNA复制和染色质修复的调节是重要的。然而，由于缺乏体内和体外研究，目前对六酶体知之甚少。由于制备纯化的六酶体的困难，六酶体的生物化学和结构研究受到阻碍。在本研究中，我们成功地重建六酶体，使用重组人组蛋白。微球菌核酸酶处理和体外重建测定显示，六酶体紧紧包裹约110个碱基对的DNA，比典型核小体内包裹的DNA的长度短约40个碱基对。小角X射线散射分析表明，六体的整体结构类似于典型的核小体。我们的研究表明，八酶体可以转化为六酶体的驱逐的H2 A/H2 B二聚体之一，并释放约40个碱基对的DNA，而不涉及大的结构变化的核小体核心颗粒。
Genomic DNA is packaged into chromatin in eukaryotes, and the nucleosome is the fundamental unit of chromatin. The canonical nucleosome is the octasome, which is composed of two H2A/H2B dimers and two H3/H4 dimers. During transcription elongation, one of the H2A/H2B dimers is removed from the octasome. The depletion of the H2A/H2B dimer is also suggested to occur during DNA replication and repair. The remaining histone components are believed to maintain a nucleosomal structure called a "hexasome", which is probably important for the regulation of gene expression, DNA replication, and repair in chromatin. However, hexasomes are currently poorly understood, due to the lack of in vivo and in vitro studies. Biochemical and structural studies of hexasomes have been hampered by the difficulty of preparing purified hexasomes. In the present study, we successfully reconstituted hexasomes, using recombinant human histones. A micrococcal nuclease treatment and in vitro reconstitution assays revealed that the hexasome tightly wraps approximately 110 base-pairs of DNA, about 40 base-pairs shorter than the length of the DNA wrapped within the canonical nucleosome. A small-angle X-ray scattering analysis revealed that the global structure of the hexasome is similar to that of the canonical nucleosome. Our studies suggest that octasomes can be converted into hexasomes by the eviction of one of the H2A/H2B dimers, and the release of about 40 base-pairs of DNA, without involving large structural changes in the nucleosome core particle.