Nucleosomes containing the histone variant H2A.Bbd organize only 118 base pairs of DNA
Nucleosomes containing the histone variant H2A.Bbd organize only 118 base pairs of DNA
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DOI：
10.1038/sj.emboj.7600316
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发表时间：
2004-08-18
期刊：
影响因子：
11.4
通讯作者：
Luger, K
中科院分区：
文献类型：
--
作者：
Bao, YH;Konesky, K;Luger, K
Bbd是一种不常见的组蛋白变异体，其序列与主要的H2A相比仅保守48%。主要的序列差异在于连接H_2A-H_2B二聚体和(H_3-H_4)(2)四聚体的对接结构域；此外，H_2A_Bbd中没有C-末端。我们组装了H_2A被H_2A取代的核小体BBD-NCP(BBD-NCP)，发现BBD-NCP具有更宽松的结构，其中只有118+/-2bp的DNA被微球菌核酸酶消化。BBD-NCP中DNA末端之间没有荧光共振能量转移，表明DNA末端之间的距离显著增加。正如域交换实验所示，BBD扩展域在很大程度上应对此行为负责。含有BBD的核小体阵列抑制来自自然启动子的转录，这种抑制可以被转录激活剂TAX和CREB缓解。这里描述的BBD-NCP的结构特性对于这个组蛋白变体的体内功能具有重要的意义，并且与它在转录活性染色质中的作用是一致的。
H2A.Bbd is an unusual histone variant whose sequence is only 48% conserved compared to major H2A. The major sequence differences are in the docking domain that tethers the H2A-H2B dimer to the (H3-H4)(2) tetramer; in addition, the C-terminal tail is absent in H2A.Bbd. We assembled nucleosomes in which H2A is replaced by H2A.Bbd (Bbd-NCP), and found that Bbd-NCP had a more relaxed structure in which only 118+/-2bp of DNA is protected against digestion with micrococcal nuclease. The absence of fluorescence resonance energy transfer between the ends of the DNA in Bbd-NCP indicates that the distance between the DNA ends is increased significantly. The Bbd docking domain is largely responsible for this behavior, as shown by domain-swap experiments. Bbd-containing nucleosomal arrays repress transcription from a natural promoter, and this repression can be alleviated by transcriptional activators Tax and CREB. The structural properties of Bbd-NCP described here have important implications for the in vivo function of this histone variant and are consistent with its proposed role in transcriptionally active chromatin.