The nucleosome serves as a general gene repressor, preventing all initiation of transcription except that which is brought about by specific positive regulatory mechanisms. The positive mechanisms begin with chromatin-remodeling by complexes that slide, disrupt, or otherwise alter the structure and organization of nucleosomes. RSC in yeast and its counterpart PBAF in human cells are the major remodeling complexes for transcription. RSC creates a nucleosome-free region in front of a gene, flanked by strongly positioned +1 and −1 nucleosomes, with the transcription start site typically 10–15 bp inside the border of the +1 nucleosome. RSC also binds stably to nucleosomes harboring regulatory elements and to +1 nucleosomes, perturbing their structures in a manner that partially exposes their DNA sequences. The cryo-electron microscope structure of a RSC–nucleosome complex reveals such a structural perturbation, with the DNA largely unwrapped from the nucleosome and likely interacting with a positively charged surface of RSC. Such unwrapping both exposes the DNA and enables its translocation across the histone octamer of the nucleosome by an ATP-dependent activity of RSC. Genetic studies have revealed additional roles of RSC in DNA repair, chromosome segregation, and other chromosomal DNA transactions. These functions of RSC likely involve the same fundamental activities, DNA unwrapping and DNA translocation.

中文翻译：

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用于转录的染色质重塑

核小体作为一种通用的基因阻遏物，阻止所有转录的启动，除非是由特定的正调节机制引起的。积极的机制始于通过滑动、破坏或以其他方式改变核小体结构和组织的复合物的染色质重塑。酵母中的 RSC 及其在人类细胞中的对应物 PBAF 是转录的主要重塑复合物。RSC 在基因前面产生一个无核小体区域，两侧是强定位的 +1 和 -1 核小体，转录起始位点通常在 +1 核小体边界内 10-15 bp。RSC 还与含有调节元件的核小体和 +1 核小体稳定结合，以部分暴露其 DNA 序列的方式扰乱它们的结构。RSC-核小体复合物的低温电子显微镜结构揭示了这种结构扰动，DNA 大部分从核小体上解开，并可能与 RSC 带正电荷的表面相互作用。这种展开既暴露了 DNA，又通过 RSC 的 ATP 依赖性活性使其易位穿过核小体的组蛋白八聚体。遗传学研究揭示了 RSC 在 DNA 修复、染色体分离和其他染色体 DNA 交易中的其他作用。RSC 的这些功能可能涉及相同的基本活动、DNA 解包和 DNA 易位。这种展开既暴露了 DNA，又通过 RSC 的 ATP 依赖性活性使其易位穿过核小体的组蛋白八聚体。遗传学研究揭示了 RSC 在 DNA 修复、染色体分离和其他染色体 DNA 交易中的其他作用。RSC 的这些功能可能涉及相同的基本活动、DNA 解包和 DNA 易位。这种展开既暴露了 DNA，又通过 RSC 的 ATP 依赖性活性使其易位穿过核小体的组蛋白八聚体。遗传学研究揭示了 RSC 在 DNA 修复、染色体分离和其他染色体 DNA 交易中的其他作用。RSC 的这些功能可能涉及相同的基本活动、DNA 解包和 DNA 易位。