Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.
Elife. 2020 Nov 10;9:e59889. doi: 10.7554/eLife.59889.
The organization of chromatin into higher order structures is essential for chromosome segregation, the repair of DNA-damage, and the regulation of gene expression. Using Micro-C XL to detect chromosomal interactions, we observed the pervasive presence of cohesin-dependent loops with defined positions throughout the genome of budding yeast, as seen in mammalian cells. In early S phase, cohesin stably binds to cohesin associated regions (CARs) genome-wide. Subsequently, positioned loops accumulate with CARs at the bases of the loops. Cohesin regulators Wpl1 and Pds5 alter the levels and distribution of cohesin at CARs, changing the pattern of positioned loops. From these observations, we propose that cohesin with loop extrusion activity is stopped by preexisting CAR-bound cohesins, generating positioned loops. The patterns of loops observed in a population of wild-type and mutant cells can be explained by this mechanism, coupled with a heterogeneous residency of cohesin at CARs in individual cells.
染色质高级结构的组织对于染色体分离、DNA 损伤修复和基因表达调控至关重要。使用 Micro-C XL 检测染色体相互作用，我们观察到在芽殖酵母的整个基因组中存在普遍存在的黏合蛋白依赖性环，这与哺乳动物细胞中的情况类似。在早期 S 期，黏合蛋白稳定地结合到全基因组的黏合蛋白相关区域 (CARs)。随后，定位环与 CARs 在环的底部积累。黏合蛋白调节剂 Wpl1 和 Pds5 改变 CARs 处黏合蛋白的水平和分布，改变定位环的模式。根据这些观察结果，我们提出具有环挤出活性的黏合蛋白被预先存在的 CAR 结合的黏合蛋白阻止，从而产生定位环。通过这种机制，再加上黏合蛋白在单个细胞中 CAR 上的异质居留，我们可以解释在野生型和突变细胞群体中观察到的环模式。
