Dependency of ISW1a chromatin remodeling on extranucleosomal DNA
Dependency of ISW1a chromatin remodeling on extranucleosomal DNA
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DOI：
10.1128/mcb.01731-06
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发表时间：
2007-04-01
影响因子：
5.3
通讯作者：
Bartholomew, Blaine
中科院分区：
文献类型：
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作者：
Gangaraju, Vamsi K.;Bartholomew, Blaine
ISW1a的核小体重塑活性取决于ISW1a是否与一个或两个核外体dna结合。ISW1a优先结合的核小体的最佳长度为33 - 35bp的核外体DNA在进入和退出位点，而核外体DNA只有一个进入或退出位点。在其中一个进入/退出位点具有核外体DNA的核小体很容易被ISW1a重塑并刺激ISW1a的atp酶活性，而相反，在两个进入/退出位点具有核外体DNA的核小体既不能刺激ISW1a的atp酶活性，也不能被动员。DNA足迹显示，核小体之间的主要构象差异是缺乏ISW1a结合核小体DNA从二联体轴两个螺旋旋转的核小体与核外体DNA在两个进入/退出位点。当ISW1a与一个或两个核外体DNA结合时，发现ISW1a的Ioc3亚基是与核外体DNA相关的主要亚基。ISW1a-核小体复合物的这两种构象被认为是ISW1a在核小体阵列上核小体间距活性的分子基础。ISW1b是ISWI的另一种异构体，它不像ISW1a那样依赖额外的核小体DNA，同样也不能分隔核小体。
The nucleosome remodeling activity of ISW1a was dependent on whether ISW1a was bound to one or both extranucleosomal DNAs. ISW1a preferentially bound nucleosomes with an optimal length of similar to 33 to 35 bp of extranucleosomal DNA at both the entry and exit sites over nucleosomes with extranucleosomal DNA at only one entry or exit site. Nucleosomes with extranucleosomal DNA at one of the entry/exit sites were readily remodeled by ISW1a and stimulated the ATPase activity of ISW1a, while conversely, nucleosomes with extranucleosomal DNA at both entry/exit sites were unable either to stimulate the ATPase activity of ISW1a or to be mobilized. DNA footprinting revealed that a major conformational difference between the nucleosomes was the lack of ISW1a binding to nucleosomal DNA two helical turns from the dyad axis in nucleosomes with extranucleosomal DNA at both entry/exit sites. The Ioc3 subunit of ISW1a was found to be the predominant subunit associated with extranucleosomal DNA when ISW1a is bound either to one or to both extranucleosomal DNAs. These two conformations of the ISW1a-nucleosome complex are suggested to be the molecular basis for the nucleosome spacing activity of ISW1a on nucleosomal arrays. ISW1b, the other isoform of ISWI, does not have the same dependency for extra nucleosomal DNA as ISW1a and, likewise, is not able to space nucleosomes.