Bömeke Katrin, Pries Ralph, Korte Virginia, Scholz Eva, Herzog Britta, Schulze Florian, Braus Gerhard H
Institute of Microbiology and Genetics, Georg August University, D-37077 Göttingen, Germany.
Mol Biol Cell. 2006 Jul;17(7):2952-62. doi: 10.1091/mbc.e05-10-0975. Epub 2006 Apr 12.
Protein stability of the c-jun-like yeast bZIP transcriptional activator Gcn4p is exclusively controlled in the yeast nucleus. Phosphorylation by the nuclear Pho85p cyclin-dependent protein kinase, a functional homolog of mammalian Cdk5, initiates the Gcn4p degradation pathway in complex with the cyclin Pcl5p. We show that the initial step in Gcn4p stabilization is the dissociation of the Pho85p/Pcl5p complex. Pcl7p, another nuclear and constantly present cyclin, is required for Gcn4p stabilization and is able to associate to Pho85p independently of the activity of the Gcn4p degradation pathway. In addition, the nuclear cyclin-dependent Pho85p kinase inhibitor Pho81p is required for Gcn4p stabilization. Pho81p only interacts with Pcl5p when Gcn4p is rapidly degraded but constitutively interacts with Pcl7p. Our data suggest that Pcl7p and Pho81p are antagonists of the Pho85p/Pcl5p complex formation in a yet unknown way, which are specifically required for Gcn4p stabilization. We suggest that dissociation of the Pho85p/Pcl5p complex as initial step in Gcn4p stabilization is a prerequisite for a shift of equilibrium to an increased amount of the Pho85p/Pcl7p complexes and subsequently results in decreased Gcn4p phosphorylation and therefore increased stability of the transcription factor.
酵母bZIP转录激活因子Gcn4p的蛋白质稳定性仅在酵母细胞核中受到调控。核内Pho85p细胞周期蛋白依赖性蛋白激酶（哺乳动物Cdk5的功能同源物）的磷酸化作用，启动了与细胞周期蛋白Pcl5p形成复合物的Gcn4p降解途径。我们发现，Gcn4p稳定化的起始步骤是Pho85p/Pcl5p复合物的解离。Pcl7p是另一种在细胞核中持续存在的细胞周期蛋白，它是Gcn4p稳定化所必需的，并且能够独立于Gcn4p降解途径的活性与Pho85p结合。此外，核细胞周期蛋白依赖性Pho85p激酶抑制剂Pho81p是Gcn4p稳定化所必需的。当Gcn4p快速降解时，Pho81p仅与Pcl5p相互作用，但它与Pcl7p持续相互作用。我们的数据表明，Pcl7p和Pho81p以一种未知的方式拮抗Pho85p/Pcl5p复合物的形成，这是Gcn4p稳定化所特需的。我们认为，Pho85p/Pcl5p复合物的解离作为Gcn4p稳定化的起始步骤，是平衡向增加的Pho85p/Pcl7p复合物数量转变的前提条件，随后导致Gcn4p磷酸化减少，从而提高转录因子的稳定性。
