Department of Physiology, University of California, San Francisco, San Francisco, California, USA.
Nat Struct Mol Biol. 2013 Feb;20(2):194-201. doi: 10.1038/nsmb.2478. Epub 2013 Jan 13.
Sister-chromatid cohesion is established during S phase when Eco1 acetylates cohesin. In budding yeast, Eco1 activity falls after S phase due to Cdk1-dependent phosphorylation, which triggers ubiquitination by SCF(Cdc4). We show here that Eco1 degradation requires the sequential actions of Cdk1 and two additional kinases, Cdc7-Dbf4 and the GSK-3 homolog Mck1. These kinases recognize motifs primed by previous phosphorylation, resulting in an ordered sequence of three phosphorylation events on Eco1. Only the latter two phosphorylation sites are spaced correctly to bind Cdc4, resulting in strict discrimination between phosphates added by Cdk1 and by Cdc7. Inhibition of Cdc7 by the DNA damage response prevents Eco1 destruction, allowing establishment of cohesion after S phase. This elaborate regulatory system, involving three independent kinases and stringent substrate selection by a ubiquitin ligase, enables robust control of cohesion establishment during normal growth and after stress.
姐妹染色单体黏合是在 S 期形成的，此时 Eco1 乙酰化黏合蛋白。在芽殖酵母中，由于 Cdk1 依赖性磷酸化，Eco1 的活性在 S 期后下降，这会触发由 SCF(Cdc4)介导的泛素化。我们在这里表明，Eco1 的降解需要 Cdk1 和另外两种激酶 Cdc7-Dbf4 和 GSK-3 同源物 Mck1 的顺序作用。这些激酶识别由先前磷酸化引发的基序，导致 Eco1 上发生三个磷酸化事件的有序序列。只有后两个磷酸化位点的间隔正确，以结合 Cdc4，从而严格区分 Cdk1 和 Cdc7 所添加的磷酸基团。DNA 损伤反应对 Cdc7 的抑制可防止 Eco1 破坏，从而允许 S 期后黏合的建立。这种复杂的调控系统涉及三个独立的激酶和严格的泛素连接酶对底物的选择，可实现在正常生长和应激后对黏合建立进行强有力的控制。
