很多细胞DNA过程都要求染色体被一个名叫 “cohesin”的环形蛋白聚在一起。尽管它很重要，但这一反应以前并没有在体外被完全重现。现在，Yasuto Murayama和Frank Uhlmann用纯化的裂殖酵母蛋白成功重现了“cohesin”加载。他们的数据让我们看到了“加载体复合物”是怎样介导“cohesin”在DNA上的拓扑结合的，同时也为对姐妹染色单体的凝聚是怎样形成的做进一步的机制性研究打下了基础。
Cohesion between sister chromatids, mediated by the chromosomal cohesin complex, is a prerequisite for faithful chromosome segregation in mitosis. Cohesin also has vital roles in DNA repair and transcriptional regulation. The ring-shaped cohesin complex is thought to encircle sister DNA strands, but its molecular mechanism of action is poorly understood and the biochemical reconstitution of cohesin activity in vitro has remained an unattained goal. Here we reconstitute cohesin loading onto DNA using purified fission yeast cohesin and its loader complex, Mis4Scc2–Ssl3Scc4 (Schizosaccharomyces pombe gene names appear throughout with their more commonly known Saccharomyces cerevisiae counterparts added in superscript). Incubation of cohesin with DNA leads to spontaneous topological loading, but this remains inefficient. The loader contacts cohesin at multiple sites around the ring circumference, including the hitherto enigmatic Psc3Scc3 subunit, and stimulates cohesin’s ATPase, resulting in efficient topological loading. The in vitro reconstitution of cohesin loading onto DNA provides mechanistic insight into the initial steps of the establishment of sister chromatid cohesion and other chromosomal processes mediated by cohesion.