Phosphorylation of cohesin by PLK1 at chromosomal arms

Prior to anaphase onset, sister-chromatids are held together by cohesin complexes. PLK1-dependent phosphorylation of the cohesin subunit STAG2 (SA2) (Hauf et al. 2005) promotes dissociation of cohesins from chromosomal arms in prometaphase (Hauf et al. 2001). Besides phosphorylating STAG2, PLK1 also phosphorylates RAD21 cohesin subunit, but the phosphorylation of RAD21 is not required for the dissociation of cohesin from chromosomal arms in early mitosis (Hauf et al. 2005). There are several potential PLK1 phosphorylation sites in STAG2 and RAD21, but the exact positions of in vivo phosphorylation of STAG2 and RAD21 by PLK1 have not been explicitly established (Hauf et al. 2005). It is likely that the phosphorylation of cohesin-bound CDCA5 (Sororin) by CDK1 creates a docking site for PLK1 at threonine T159 of CDCA5, thus enabling PLK1 to phosphorylate cohesin subunits (Zhang et al. 2011).

在减数分裂期开始之前，姐妹染色单体通过连接复合物（cohesin complexes）保持连接。依赖于PLK1的磷酸化作用促使连接复合物在前期从染色体臂上解离（Hauf et al. 2005）。除了磷酸化STAG2（SA2）连接复合物亚单位外，PLK1还磷酸化RAD21连接复合物亚单位，但RAD21的磷酸化并非在早期有丝分裂中连接复合物从染色体臂上解离所必需（Hauf et al. 2005）。STAG2和RAD21中存在多个潜在的PLK1磷酸化位点，但PLK1在体内对STAG2和RAD21进行磷酸化的确切位置尚未明确建立（Hauf et al. 2005）。有研究表明，CDK1对连接复合物结合的CDCA5（Sororin）的磷酸化可能在CDCA5的苏氨酸T159处形成PLK1的结合位点，从而允许PLK1磷酸化连接复合物亚单位（Zhang et al. 2011）。