Nomoto S, Nakayama N, Arai K, Matsumoto K
Department of Molecular Biology, DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, California 94304.
EMBO J. 1990 Mar;9(3):691-6. doi: 10.1002/j.1460-2075.1990.tb08161.x.
The yeast GPA1, STE4, and STE18 genes encode proteins homologous to the respective alpha, beta and gamma subunits of the mammalian G protein complex which appears to mediate the response to mating pheromones. Overexpression of the STE4 protein by the galactose-inducible GAL1 promoter caused activation of the pheromone response pathway which resulted in cell-cycle arrest in late G1 phase and induction of the FUS1 gene expression, thereby suppressing the sterility of the receptor-less mutant delta ste2. Disruption of STE18, in turn, suppressed activation of the pheromone response induced by overexpression of STE4, suggesting that the STE18 product is required for the STE4 action. However, overexpression of both the STE4 and STE18 proteins did not generate a stronger pheromone response than overexpression of STE4 in the presence of wild-type levels of STE18. These results suggest that the beta subunit is the limiting component for the pheromone response and support the idea that beta and gamma subunits act as a positive regulator. Furthermore, overexpression of GPA1 prevented cell-cycle arrest but not FUS1 induction mediated by overexpression of STE4. This implies that the alpha subunit acts as a negative regulator presumably through interacting with beta and gamma subunits in the mating pheromone signaling pathway.
酵母的GPA1、STE4和STE18基因编码的蛋白质分别与哺乳动物G蛋白复合物的α、β和γ亚基同源，该复合物似乎介导了对交配信息素的反应。由半乳糖诱导型GAL1启动子过度表达STE4蛋白会导致信息素反应途径的激活，从而导致细胞周期在G1期后期停滞，并诱导FUS1基因表达，进而抑制无受体突变体δste2的不育性。相反，破坏STE18会抑制由STE4过度表达诱导的信息素反应的激活，这表明STE18产物是STE4发挥作用所必需的。然而，在STE18处于野生型水平时，同时过度表达STE4和STE18蛋白并不会比单独过度表达STE4产生更强的信息素反应。这些结果表明β亚基是信息素反应的限制成分，并支持β和γ亚基作为正调节因子的观点。此外，过度表达GPA1可防止由过度表达STE4介导的细胞周期停滞，但不能阻止FUS1诱导。这意味着α亚基可能通过在交配信息素信号通路中与β和γ亚基相互作用而作为负调节因子。
