Condensin mediates chromosome condensation, which is essential for proper chromosome segregation during mitosis. Prior to anaphase of budding yeast, the ribosomal DNA (RDN) condenses to a thin loop that is distinct from the rest of the chromosomes. We provide evidence that the establishment and maintenance of this RDN condensation requires the regulation of condensin by Cdc5p (polo) kinase. We show that Cdc5p is recruited to the site of condensin binding in the RDN by cohesin, a complex related to condensin. Cdc5p and cohesin prevent condensin from misfolding the RDN into an irreversibly decondensed state. From these and other observations, we propose that the spatial regulation of Cdc5p by cohesin modulates condensin activity to ensure proper RDN folding into a thin loop. This mechanism may be evolutionarily conserved, promoting the thinly condensed constrictions that occur at centromeres and RDN of mitotic chromosomes in plants and animals.

中文翻译：

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染色体凝缩中凝缩蛋白活性的空间调控。


凝缩蛋白介导染色体凝缩，这对于有丝分裂过程中正确的染色体分离至关重要。在芽殖酵母进入后期之前，核糖体 DNA (RDN) 凝结成一个与染色体其余部分不同的细环。我们提供的证据表明，这种 RDN 缩合的建立和维持需要 Cdc5p (polo) 激酶对缩合蛋白的调节。我们发现，Cdc5p 被粘连蛋白（一种与凝缩蛋白相关的复合物）招募到 RDN 中凝缩蛋白结合的位点。 Cdc5p 和粘连蛋白可防止凝缩蛋白将 RDN 错误折叠成不可逆的解凝状态。根据这些和其他观察结果，我们提出粘连蛋白对 Cdc5p 的空间调节调节凝缩蛋白活性，以确保 RDN 正确折叠成细环。这种机制可能在进化上是保守的，促进植物和动物有丝分裂染色体着丝粒和 RDN 处发生的稀薄压缩。