Huang S, Jeffery D A, Anthony M D, O'Shea E K
Department of Biochemistry & Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California 94143-0448, USA.
Mol Cell Biol. 2001 Oct;21(19):6695-705. doi: 10.1128/MCB.21.19.6695-6705.2001.
In response to phosphate limitation, Saccharomyces cerevisiae induces transcription of a set of genes important for survival. A phosphate-responsive signal transduction pathway mediates this response by controlling the activity of the transcription factor Pho4. Three components of this signal transduction pathway resemble those used to regulate the eukaryotic cell cycle: a cyclin-dependent kinase (CDK), Pho85; a cyclin, Pho80; and a CDK inhibitor (CKI), Pho81. Pho81 forms a stable complex with Pho80-Pho85 under both high- and low-phosphate conditions, but it only inhibits the kinase when cells are starved for phosphate. Pho81 contains six tandem repeats of the ankyrin consensus domain homologous to the INK4 family of mammalian CKIs. INK4 proteins inhibit kinase activity through an interaction of the ankyrin repeats and the CDK subunits. Surprisingly, we find that a region of Pho81 containing 80 amino acids C terminal to the ankyrin repeats is necessary and sufficient for Pho81's CKI function. The ankyrin repeats of Pho81 appear to have no significant role in Pho81 inhibition. Our results suggest that Pho81 inhibits Pho80-Pho85 with a novel motif.
为应对磷酸盐限制，酿酒酵母会诱导一组对生存至关重要的基因转录。一条磷酸盐应答信号转导途径通过控制转录因子Pho4的活性来介导这种应答。该信号转导途径的三个组分类似于用于调控真核细胞周期的组分：一个细胞周期蛋白依赖性激酶（CDK），Pho85；一个细胞周期蛋白，Pho80；以及一个CDK抑制剂（CKI），Pho81。在高磷酸盐和低磷酸盐条件下，Pho81都与Pho80-Pho85形成稳定复合物，但只有当细胞处于磷酸盐饥饿状态时它才会抑制激酶活性。Pho81含有与哺乳动物CKI的INK4家族同源的锚蛋白共有结构域的六个串联重复序列。INK4蛋白通过锚蛋白重复序列与CDK亚基的相互作用来抑制激酶活性。令人惊讶的是，我们发现Pho81中位于锚蛋白重复序列C端的一个含80个氨基酸的区域对于Pho81的CKI功能是必需且充分的。Pho81的锚蛋白重复序列在Pho81的抑制作用中似乎没有显著作用。我们的结果表明，Pho81通过一个新的基序抑制Pho80-Pho85。
