G Protein Regulation of a Microtubule Motor Protein in Yeast

细胞极化对形态发生、免疫反应、神经元发育、趋化性和运动性是必不可少的。酿酒酵母是一个研究广泛的真核生物模型，它表现出许多极化现象，包括信号诱导的细胞形状和核位置的变化。在其生命周期的单倍体阶段，酵母细胞分泌多肽信息素，将相反交配型的营养生长细胞转化为配子。信息素为细胞和核融合做准备，它触发向交配伙伴的极化生长(趋化性)，并将细胞核迁移到交配突起的尖端。最近的结果表明，信息素响应的G-α蛋白Gpa1参与了信号诱导的极化生长和核运动的控制。在对信息素做出反应的细胞中，Gpa1直接与交配特异的MAPK蛋白Fus3和Kar3相互作用，Kar3是一种微管马达蛋白，在交配过程中对核运动至关重要。Gpa1-Fus3相互作用的中断会导致趋化性、微管定向和核迁移方面的缺陷。这个项目的长期目标是了解Gα蛋白如何调节微管细胞骨架以响应外部信号。为此，将使用遗传、生化、质谱学和成像方法来确定Gpa1如何影响Kar3的交配特异性功能，以及Fus3是否参与了这一调控。由于Gpa1和Kar3提供了第一个Gα蛋白/马达-蛋白质相互作用的例子，而且Gα对核运动的调节是史无前例的，这一分析有望提供信息。该项目还将提供重要的培训机会。一名研究生和一名博士后将致力于这项研究的几个方面。此外，每年暑假还将招募一名高中生参与该项目。

Cellular polarization is essential to morphogenesis, immune response, neuronal development, chemotropism, and motility. Saccharomyces cerevisiae is a well-studied model eukaryote that exhibits numerous polarization phenomena, including signal-induced changes in cell shape and nuclear position. During the haploid phase of their life cycle, yeast cells secrete peptide pheromones that transform vegetatively growing cells of opposite mating type into gametes. Preparatory to cellular and nuclear fusion, pheromone triggers polarized growth toward the mating partner (chemotropism), and migration of the nucleus to the tip of the mating projection. Recent results implicate the pheromone-responsive G-alpha protein, Gpa1, in the control of signal-induced polarized growth and nuclear movement. In cells responding to pheromone, Gpa1 interacts directly with the mating-specific MAPK protein, Fus3, and with Kar3, a microtubule motor protein that is essential for nuclear movement during mating. Disruption of the Gpa1-Fus3 interaction confers defects in chemotropism, microtubule orientation, and nuclear migration. The long-term goal of this project is to understand how G alpha proteins regulate the microtubule cytoskeleton in response to external signals. To this end, genetic, biochemical, mass spectrometric, and imaging approaches will be used to determine how Gpa1 affects the mating-specific functions of Kar3, and whether Fus3 is involved in this regulation. Because Gpa1 and Kar3 provide the first example of a G alpha protein/motor-protein interaction, and because G alpha regulation of nuclear movement is unprecedented, this analysis promises to be informative. This project will also provide significant training opportunity. A graduate student and a postdoctoral fellow will be working on several aspects of the research. In addition, a high school student will be recruited to participate in the project each summer.