凝聚素和凝集素在姐妹染色单体内聚和染色体分离中起着基本作用,分别。两者都由染色体(SMC)亚基的异源二聚体结构维持组成,具有头部(包含ATPase)和铰链,由长卷曲螺旋干预。非SMC亚基(凝缩素的Cnd1,Cnd2和Cnd3;粘蛋白的Rad21,Psc3和Mis4)与SMC头部结合。这里,我们报道了大量的分裂酵母凝集素和粘附素突变体的自发基因外抑制剂,它们的位点是通过全基因组测序确定的。凝缩素的非SMC亚基的突变体通过破坏SUMO化途径被拯救。的确,Cnd2,Cnd3和Cut3的SUMO化发生在有丝分裂中,和Cnd3K870在功能上与Cnd亚基相反。相比之下,通过RNA消除途径(Erh1,Mmi1和Red1)的丧失,和loader突变体mis4通过Hrp1介导的染色质重塑的丧失被拯救。此外,发现了凝集素和粘附素铰链突变体的不同规定。Kleisin亚基(Cnd2和Rad21)的N端螺旋束[包含螺旋-转角-螺旋(HTH)基序]中的突变挽救了粘附蛋白和凝缩蛋白中几乎相同的铰链界面突变,分别。这些突变可能调节Kleisin与SMC头部的卷曲螺旋的相互作用,从而揭示了一个共同的,但以前未知,铰链和卷叶素N结构域之间的抑制机制,这是成功的染色体分离所必需的。我们建议在凝集素和粘附素中,头部(或卷尾素)和铰链可以相互作用并协同调节所得的卷曲螺旋以保持和释放染色体DNA。
Cohesin and condensin play fundamental roles in sister chromatid cohesion and chromosome segregation, respectively. Both consist of heterodimeric structural maintenance of chromosomes (SMC) subunits, which possess a head (containing ATPase) and a hinge, intervened by long coiled coils. Non-SMC subunits (Cnd1, Cnd2, and Cnd3 for condensin; Rad21, Psc3, and Mis4 for cohesin) bind to the SMC heads. Here, we report a large number of spontaneous extragenic suppressors for fission yeast condensin and cohesin mutants, and their sites were determined by whole-genome sequencing. Mutants of condensin\'s non-SMC subunits were rescued by impairing the SUMOylation pathway. Indeed, SUMOylation of Cnd2, Cnd3, and Cut3 occurs in midmitosis, and Cnd3 K870 SUMOylation functionally opposes Cnd subunits. In contrast, cohesin mutants rad21 and psc3 were rescued by loss of the RNA elimination pathway (Erh1, Mmi1, and Red1), and loader mutant mis4 was rescued by loss of Hrp1-mediated chromatin remodeling. In addition, distinct regulations were discovered for condensin and cohesin hinge mutants. Mutations in the N-terminal helix bundle [containing a helix-turn-helix (HTH) motif] of
kleisin subunits (Cnd2 and Rad21) rescue virtually identical hinge interface mutations in cohesin and condensin, respectively. These mutations may regulate
kleisin\'s interaction with the coiled coil at the SMC head, thereby revealing a common, but previously unknown, suppression mechanism between the hinge and the
kleisin N domain, which is required for successful chromosome segregation. We propose that in both condensin and cohesin, the head (or
kleisin) and hinge may interact and collaboratively regulate the resulting coiled coils to hold and release chromosomal DNAs.