Cell Cycle Regulation of Glc7p Protein Phosphatase

真核细胞分裂的有序步骤部分受到及时的蛋白质降解和可逆的蛋白质磷酸化的调节。 蛋白磷酸酶-1（PP 1）酶对细胞周期去磷酸化反应很重要。 芽殖酵母，酿酒酵母，提供了已知的最简单的PP 1系统，因为它只有一个PP 1基因，GLC 7（基因产物是GlcTp）。 glc 7 p使酵母细胞周期中两个转变的关键蛋白质去磷酸化。第一，G1到S期受细胞的营养状态调节。 第二个过渡，后期之前，似乎使用GlcTp监测有丝分裂纺锤体组装，这是必要的忠实的染色体分离。 由GlcTp去磷酸化的蛋白质控制细胞周期，这是未知的。最近的研究结果表明，Glc 7 p蛋白质水平在细胞周期中振荡。 Glc 7 p的峰值水平出现在G1和S期晚期。 相反，在细胞周期间隔期间检测到低水平，其中G1或有丝分裂周期蛋白被泛素依赖性蛋白水解破坏。 因此，他们假设Glc 7 p是泛素连接酶复合物破坏细胞周期蛋白的泛素依赖性蛋白水解的靶点。 本项目的第一个目的是分析潜在的泛素依赖性Glc 7 p蛋白水解。 该提案的第二个目的是定义Glc 8 p（Glc 7 p的非催化亚基）在其调节中的作用，以观察其是否在G1期间保护Glc 7 p免受泛素化和破坏，从而使Glc 7 p使底物蛋白去磷酸化。 在Glc 7 p耗尽的细胞中发现的高细胞周期蛋白依赖性蛋白激酶（CDK）活性表明，当Glc 7 p活性降低时，S期或有丝分裂期细胞周期蛋白没有被适当地破坏。 这一发现进一步暗示了被称为后期促进复合物（APC）的泛素连接酶可能被Glc 7 p去磷酸化激活。 最后一个目的是确定负责的监管磷蛋白，Glc 7 p底物和APC regulators.Although几个磷蛋白在细胞分裂中发挥重要作用，蛋白激酶和磷酸酶，控制其磷酸化状态在很大程度上是未知的。 细胞分裂的控制是一个复杂的过程，涉及许多参与者。 初步分析表明，Glc 7 p蛋白磷酸酶在这一过程中发挥了作用。 该项目的目标是将Glc 7 p功能与细胞分裂的其他已知方面整合。

The orderly steps of eukaryotic cell division are regulated in part by timely protein degradation and reversible protein phosphorylation. Protein phosphatase-1 (PP1) enzymes are important for cell cycle dephosphorylation reactions. The budding yeast, Saccharomyces cerevisiae, offers the simplest known PP1 system because it has only a single gene for PP1, GLC7 (gene product is GlcTp). Glc7p dephosphorylates proteins critical for two transitions in the cell cycle of yeast. The first, G1 to S-phase is regulated by the nutritional status of the cells. The second transition, prior to anaphase, appears to use GlcTp to monitor the mitotic spindle assembly, which is necessary for faithful chromosome segregation. The proteins dephosphorylated by GlcTp, which control the cell cycle, are unknown.Recent results of this investigator show that Glc7p protein levels oscillate during the cell cycle. Peak levels of Glc7p were found in late G1 and S-phases. Conversely, low levels were detected during cell cycle intervals in which G1 or mitotic cyclins are destroyed by ubiquitin-dependent proteolysis. Therefore, they hypothesize that Glc7p is a target of ubiquitin-dependent proteolysis by the ubiquitin ligase complexes that destroy cyclins. The first aim of this project is to analyze potential ubiquitin-dependent Glc7p proteolysis. The second aim of this proposal defines the role of Glc8p, a noncatalytic subunit of Glc7p, in its regulation, to see if it shields Glc7p from ubiquitination and destruction during G1 to allow Glc7p to dephosphorylate substrate proteins . The high cyclin-dependent protein kinase (CDK) activity found in Glc7p-depleted cells suggests that S-phase or mitotic cyclins are not destroyed appropriately when Glc7p activity is diminished. This finding further implies the ubiquitin ligase known as the anaphase-promoting complex (APC) may be activated by Glc7p dephosphorylation. The last aim seeks to identify the responsible regulatory phosphoproteins that are Glc7p substrates and APC regulators.Although several phosphoproteins play important roles in cell division, the protein kinases and phosphatases that control their phosphorylation state are largely unknown. The control of cell division is a complicated process, which involves many participants. Preliminary analysis indicates that Glc7p protein phosphatase plays a part in this process. The goal of this project is to integrate Glc7p function with other known aspects of cell division.