PDF(Pubmed)
Abstract：
In budding yeast, the nucleolus serves as the site to sequester Cdc14, a phosphatase essential for mitotic exit. Nucleolar proteins Tof2, Net1, and Fob1 are required for this sequestration. Although it is known that these nucleolar proteins are SUMOylated, how SUMOylation regulates their activity remains unknown. Here, we show that Tof2 exhibits cell-cycle-regulated nucleolar delocalization and turnover. Depletion of the nuclear small ubiquitin-like modifier (SUMO) protease Ulp2 not only causes Tof2 polySUMOylation, nucleolar delocalization, and degradation but also leads to Cdc14 nucleolar release and activation. This outcome depends on polySUMOylation and the activity of downstream enzymes, including SUMO-targeted ubiquitin ligase and Cdc48/p97 segregase. We further developed a system to tether SUMO machinery to Tof2 and generated a SUMO-deficient tof2 mutant, and the results indicate that Tof2 polySUMOylation is necessary and sufficient for its nucleolar delocalization and degradation. Together, our work reveals a polySUMO-dependent mechanism that delocalizes Tof2 from the nucleolus to facilitate mitotic exit.
摘要：
在出芽酵母中，核仁是隔离Cdc14的位点，Cdc14是有丝分裂退出所必需的磷酸酶。该隔离需要核仁蛋白Tof2、Net1和Fob1。尽管已知这些核仁蛋白是SUMO化的，SUMO化如何调节它们的活性仍然未知。这里,我们显示Tof2表现出细胞周期调节的核仁离域和周转。核小泛素样修饰剂（SUMO）蛋白酶Ulp2的耗尽不仅会导致Tof2多聚SUMO化，核仁离域,和降解，但也导致Cdc14核仁释放和活化。这个结果取决于聚SUMO化和下游酶的活性，包括SUMO靶向泛素连接酶和Cdc48/p97分离酶。我们进一步开发了一个系统，将SUMO机器连接到Tof2，并产生了SUMO缺陷的tof2突变体，结果表明，Tof2聚SUMO化对其核仁离域和降解是必要和充分的。一起,我们的工作揭示了一种多SUMO依赖性机制，该机制使Tof2从核仁离域以促进有丝分裂退出。
