Hughes D A, Yabana N, Yamamoto M
Department of Biophysics and Biochemistry, School of Science, University of Tokyo, Japan.
J Cell Sci. 1994 Dec;107 ( Pt 12):3635-42. doi: 10.1242/jcs.107.12.3635.
The ste6 gene of Schizosaccharomyces pombe encodes a putative GDP-GTP exchange factor for the ras1 gene product. Genetic analysis of the ste6 and ras1 genes has shown that they are required for mating and for the response to mating pheromones. In this study we show that expression of the ste6-encoded mRNA is induced by nitrogen starvation, the physiological signal that triggers mating and sexual differentiation. Exposure to mating pheromones enhances the induction of ste6 expression upon nitrogen starvation. Pheromone-induced expression requires not only the function of components of the pheromone-signalling pathway, but also ras1 function. Furthermore, mutants in which the Ras1 protein is activated have higher basal and induced levels of ste6 gene expression than wild-type cells. These observations indicate the existence of a positive-feedback loop through which Ras1 stimulates the expression of its own activator. Since Ste6 is likely to promote the exchange of guanine nucleotides on Ras1 protein, our results suggest an important role for GDP-GTP exchange in the regulation of Ras1 activity during the mating process in S. pombe.
粟酒裂殖酵母的ste6基因编码一种假定的ras1基因产物的GDP - GTP交换因子。对ste6和ras1基因的遗传分析表明，它们对于交配以及对交配信息素的反应是必需的。在本研究中，我们表明ste6编码的mRNA的表达是由氮饥饿诱导的，氮饥饿是触发交配和有性分化的生理信号。暴露于交配信息素会增强氮饥饿时ste6表达的诱导。信息素诱导的表达不仅需要信息素信号通路成分的功能，还需要ras1的功能。此外，Ras1蛋白被激活的突变体比野生型细胞具有更高的ste6基因基础表达水平和诱导表达水平。这些观察结果表明存在一个正反馈环，通过该正反馈环Ras1刺激其自身激活剂的表达。由于Ste6可能促进Ras1蛋白上鸟嘌呤核苷酸的交换，我们的结果表明GDP - GTP交换在粟酒裂殖酵母交配过程中Ras1活性的调节中起重要作用。
