Department of Biochemistry and Biophysics, University of Rochester Medical Center, 601 Elmwood Ave., Rochester, NY 14642, USA.
Mol Cell Biol. 2011 Oct;31(20):4165-75. doi: 10.1128/MCB.05605-11. Epub 2011 Aug 22.
The multisubunit SWI/SNF and RSC complexes utilize energy derived from ATP hydrolysis to mobilize nucleosomes and render the DNA accessible for various nuclear processes. Here we test the idea that remodeling involves intermediates with mobile DNA bulges or loops within the nucleosome by cross-linking the H2A N- or C-terminal tails together to generate protein "loops" that constrict separation of the DNA from the histone surface. Analyses indicate that this intranucleosomal cross-linking causes little or no change in remodeling-dependent exposure of DNA sequences within the nucleosome to restriction enzymes. However, cross-linking inhibits nucleosome mobilization and blocks complete movement of nucleosomes to extreme end positions on the DNA fragments. These results are consistent with evidence that nucleosome remodeling involves intermediates with DNA loops on the nucleosome surface but indicate that such loops do not freely diffuse about the surface of the histone octamer. We propose a threading model for movement of DNA loops around the perimeter of the nucleosome core.
多亚基 SWI/SNF 和 RSC 复合物利用 ATP 水解产生的能量来移动核小体，使 DNA 能够进行各种核过程。在这里，我们通过交联 H2A N- 或 C- 末端尾巴来测试重塑涉及带有移动 DNA 膨出或环的中间物的想法，从而产生限制 DNA 与组蛋白表面分离的蛋白质“环”。分析表明，这种核内交联几乎不会改变核小体中受重塑影响的 DNA 序列对限制酶的暴露。然而，交联会抑制核小体的迁移，并阻止核小体完全移动到 DNA 片段的极端末端位置。这些结果与核小体重塑涉及核小体表面带有 DNA 环的中间物的证据一致，但表明这种环不会在组蛋白八聚体表面自由扩散。我们提出了一种 DNA 环在核小体核心周围移动的穿线模型。
