Structural maintenance of chromosomes (SMC) protein complexes are key determinants of chromosome conformation. Using Hi-C and polymer modelling, we study how cohesin and condensin, two deeply conserved SMC complexes, organize chromosomes in the budding yeast Saccharomyces cerevisiae. The canonical role of cohesin is to co-align sister chromatids, while condensin generally compacts mitotic chromosomes. We find strikingly different roles for the two complexes in budding yeast mitosis. First, cohesin is responsible for compacting mitotic chromosome arms, independently of sister chromatid cohesion. Polymer simulations demonstrate that this role can be fully accounted for through cis-looping of chromatin. Second, condensin is generally dispensable for compaction along chromosome arms. Instead, it plays a targeted role compacting the rDNA proximal regions and promoting resolution of peri-centromeric regions. Our results argue that the conserved mechanism of SMC complexes is to form chromatin loops and that distinct SMC-dependent looping activities are selectively deployed to appropriately compact chromosomes.

中文翻译：

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SMC复合物根据基因组背景差异压实有丝分裂染色体

染色体（SMC）蛋白复合物的结构维持是染色体构象的关键决定因素。使用Hi-C和聚合物建模，我们研究了粘连蛋白和凝缩蛋白，这两个深度保守的SMC复合物如何在萌芽的酿酒酵母中组织染色体。粘着蛋白的典型作用是使姐妹染色单体共对齐，而凝缩蛋白通常压紧有丝分裂染色体。我们发现两种复合物在发芽酵母有丝分裂中的作用截然不同。首先，粘着蛋白负责压紧有丝分裂染色体臂，独立于姐妹染色单体粘着。聚合物模拟表明，可以通过顺式充分说明这一作用-染色质的环化。其次，凝集素通常对于沿染色体臂的紧缩是必不可少的。取而代之的是，它起着紧缩rDNA近端区域并促进着中着丝粒区域分辨率的目标作用。我们的研究结果表明，SMC复合物的保守机制是形成染色质环，不同的SMC依赖性环化活性被选择性地部署到适当紧凑的染色体上。