The CDK Activation Network of Fission Yeast

描述（由申请人提供）：拟议的研究的长期目标是了解一个周期独立激酶（CDKs）和上游cdk激活激酶（CAKs）网络如何协调细胞分裂与基因表达，以及在一种模式真核生物分裂酵母Schizosaccharomyces pombe中基因组完整性的维持。在裂变酵母中，和在多细胞生物中一样，一种激酶激活主细胞周期CDK （Cdk1）来驱动细胞分裂，并磷酸化RNA聚合酶II来调节转录周期。与人类cdk7同源的mcs6酶与另一种CDK Cdk9一起控制与细胞周期相关的基因表达程序，并协调RNA分子的合成及其加工过程，以产生可翻译成蛋白质的成熟信使RNA （mrna）。S. pombe还含有第二个CAK， Csk1，它对生存能力是必不可少的，但可以激活Cdk1， Mcs6和Cdk9。缺乏Csk1的细胞存在生长缺陷，并且对dna损伤剂和复制抑制剂极度敏感。因此，CAK-CDK网络通过多种途径发出信号，除了具有促进细胞增殖的典型功能外，还在基因表达和基因组监测中发挥关键的调节作用。我们将结合生物化学和遗传学的方法来剖析裂变酵母中CAK-CDK网络的功能和靶点。通过引入易受特殊设计的小分子抑制的每个CDK的基因工程版本，我们能够在体内关闭激酶活性，并测量细胞增殖和基因表达的后果。同样的操作也使我们能够识别目标激酶的蛋白质底物。具体目标是：

DESCRIPTION (provided by applicant): The long-term goal of the proposed research is to understand how a network of cyclindependent kinases (CDKs) and upstream CDK-activating kinases (CAKs) coordinates cell division with gene expression and the maintenance of genome integrity in a model eukaryotic organism, the fission yeast Schizosaccharomyces pombe. In fission yeast, as in multicellular organisms, one kinase activates the major cell-cycle CDK (Cdk1) to drive cell division and phosphorylates RNA polymerase II to regulate the transcription cycle. That enzyme-Mcs6, which is homologous to human Cdk7-works together with another CDK, Cdk9, to control gene expression programs linked to the cell cycle, and to coordinate synthesis of RNA molecules with their processing to produce mature messenger RNAs (mRNAs) that can be translated into proteins. S. pombe also contains a second CAK, Csk1, which is dispensable for viability, but which activates Cdk1, Mcs6 and Cdk9. Cells lacking Csk1 have growth defects and are hypersensitive to DNA-damaging agents and replication inhibitors. The CAK-CDK network therefore signals through multiple pathways, and plays critical regulatory roles in gene expression and genomic surveillance, in addition to its canonical function in promoting cell proliferation. We will combine biochemical and genetic approaches to dissect the functions and targets of the CAK-CDK network in fission yeast. By introducing a genetically engineered version of each CDK that is susceptible to inhibition by a specially designed small molecule, we are able to switch kinase activity off in vivo, and measure the consequences for cell proliferation and gene expression. The same manipulation also allows us to identify the protein substrates of the targeted kinase. The specific aims are: 1. To investigate coordination between Mcs6 (Cdk7) and Cdk9, which act sequentially and in concert to control expression of select genes. We will investigate whether Cdk9 recruitment or activity in transcription elongation complexes depends on prior function of Mcs6. 2. To investigate the coupling of transcription (synthesis) of mRNAs with their maturation by a complex containing Cdk9 and an essential mRNA-processing enzyme, the mRNA 5'-cap methyltransferase Pcm1. 3. To identify new targets and functions of CAKs and CDKs in the DNA damage response. PUBLIC HEALTH RELEVANCE: The integrating function of the CAK-CDK network is conserved in human cells, and potentially disrupted in cancer, where impaired control of cell proliferation, derangement of gene expression and damage to the genome all contribute to the initiation and progression of tumors. If we are to block or inhibit functions of this pathway in order to stop growth and division of tumor cells, an understanding of its multiple functions will be needed to avoid toxicity to normal tissue. The powerful genetic tools available in fission yeast, and the fundamental conservation of pathway function and organization with humans, make S. pombe the ideal model system in which to perform this work.