Trautmann Susanne, McCollum Dannel
Department of Molecular Genetics and Microbiology, University of Massachusetts Medical Center, Worcester, Massachusetts 01605, USA.
Curr Biol. 2005 Aug 9;15(15):1384-9. doi: 10.1016/j.cub.2005.06.039.
Cdc14-like phosphatases regulate a variety of cell cycle events by dephosphorylating CDK sites. Their cell cycle-dependent changes in localization may be important to carry out distinct functions. Work in budding and fission yeast suggested that Cdc14-like phosphatases are inhibited by nucleolar sequestration. In S. cerevisiae, Cdc14p is released from the nucleolus by the FEAR network and Cdk1, whereas the S. pombe CDC14-like phosphatase Clp1p (also known as Flp1p) is released at mitotic entry by an unknown mechanism. The mitotic exit network (MEN) in S. cerevisiae and its homologous network, the septation initiation network (SIN), in S. pombe act through an unknown mechanism to keep the phosphatase out of the nucleolus in late mitosis. SIN-dependent cytoplasmic maintenance of Clp1p is thought to be essential for the cytokinesis checkpoint, which blocks further rounds of nuclear division until cytokinesis is completed. By targeting Clp1p to the nucleus or the cytoplasm, we demonstrate distinct functions for these pools of Clp1p in chromosome segregation and cytokinesis, respectively. Our results further suggest that the SIN does not keep Clp1p out of the nucleolus by regulating nucleolar affinity, as proposed for S. cerevisiae Cdc14p, but instead, Clp1p may be regulated by nuclear import/export.
Cdc14样磷酸酶通过使CDK位点去磷酸化来调节多种细胞周期事件。它们在细胞周期中定位的变化对于执行不同的功能可能很重要。在芽殖酵母和裂殖酵母中的研究表明，Cdc14样磷酸酶受到核仁隔离的抑制。在酿酒酵母中，Cdc14p通过FEAR网络和Cdk1从核仁中释放出来，而裂殖酵母中与Cdc14类似的磷酸酶Clp1p（也称为Flp1p）在有丝分裂开始时通过未知机制释放。酿酒酵母中的有丝分裂退出网络（MEN）及其在裂殖酵母中的同源网络隔膜起始网络（SIN），通过未知机制在有丝分裂后期将磷酸酶排除在核仁之外。Clp1p依赖SIN的细胞质维持被认为对胞质分裂检查点至关重要，该检查点会阻止进一步的核分裂轮次，直到胞质分裂完成。通过将Clp1p靶向细胞核或细胞质，我们分别证明了这些Clp1p池在染色体分离和胞质分裂中的不同功能。我们的结果进一步表明，SIN并不像酿酒酵母Cdc14p那样通过调节核仁亲和力将Clp1p排除在核仁之外，相反，Clp1p可能受核输入/输出的调节。
