NAP1 modulates binding of linker histone H1 to chromatin and induces an extended chromatin fiber conformation
NAP1 modulates binding of linker histone H1 to chromatin and induces an extended chromatin fiber conformation
复制标题
DOI：
10.1074/jbc.m507322200
复制
发表时间：
2005-10-07
影响因子：
4.8
通讯作者：
Rippe, K
中科院分区：
文献类型：
--
作者：
Kepert, JF;Mazurkiewicz, J;Rippe, K
NAP1（核小体组装蛋白1）是一种组蛋白伴侣，在组蛋白进入细胞核、核小体组装/重塑和转录过程中，NAP1主要与细胞内的组蛋白H2A中心点H2B二聚体结合。这里研究了NAP1如何与HeLa细胞分离的染色质纤维相互作用。通过沉降速度超离心实验证明，NAP1诱导了向延伸纤维构象的可逆变化。这种转变是由于连接蛋白H1的去除。H2A中心点H2B二聚体仍然稳定地结合到天然纤维片段和缺乏连接蛋白H1的纤维上。这与单核核小体底物相反，单核核小体显示nap1诱导从核心颗粒中去除单个H2A中心点H2B二聚体。采用扫描/原子力显微镜观察了NAP1对染色质纤维结构的影响。对36,000个核小体的定量图像分析显示，核小体间的平均距离从22.3 +/- 0.4 nm增加到27.6 +/- 0.6 nm，而整体纤维结构保持不变。这一变化反映了H1与NAP1结合导致的染色体解体，因为从H1剥离的染色质纤维显示平均核小体距离为27.4 +/- 0.8 nm。研究结果表明，NAP1可能通过调节局部连接体组蛋白含量，参与转录和复制的染色质重塑过程。
NAP1 ( nucleosome assembly protein 1) is a histone chaperone that has been described to bind predominantly to the histone H2A center dot H2B dimer in the cell during shuttling of histones into the nucleus, nucleosome assembly/ remodeling, and transcription. Here it was examined how NAP1 interacts with chromatin fibers isolated from HeLa cells. NAP1 induced a reversible change toward an extended fiber conformation as demonstrated by sedimentation velocity ultracentrifugation experiments. This transition was due to the removal of the linker histone H1. The H2A center dot H2B dimer remained stably bound to the native fiber fragments and to fibers devoid of linker histone H1. This was in contrast to mononucleosome substrates, which displayed a NAP1-induced removal of a single H2A center dot H2B dimer from the core particle. The effect of NAP1 on the chromatin fiber structure was examined by scanning/ atomic force microscopy. A quantitative image analysis of similar to 36,000 nucleosomes revealed an increase of the average internucleosomal distance from 22.3 +/- 0.4 to 27.6 +/- 0.6 nm, whereas the overall fiber structure was preserved. This change reflects the disintegration of the chromatosome due to binding of H1 to NAP1 as chromatin fibers stripped from H1 showed an average nucleosome distance of 27.4 +/- 0.8 nm. The findings suggest a possible role of NAP1 in chromatin remodeling processes involved in transcription and replication by modulating the local linker histone content.