Mirisola Mario G, Gallo Alessia, De Leo Giacomo
Dipartimento di Biopatologia e Metodologie Biomediche, Via Divisi, 83, Università degli studi di Palermo, 90133 Palermo, Italy.
FEBS Lett. 2007 May 15;581(10):2009-16. doi: 10.1016/j.febslet.2007.04.018. Epub 2007 Apr 23.
In the yeast Saccharomyces cerevisiae the genes involved in galactose metabolism (GAL1,7,10) are transcriptionally activated more than a 1000-fold in the presence of galactose as the sole carbon source in the culture media. In the present work, we monitored the activity of the GAL10 gene promoter in different Ras-cAMP genetic backgrounds. We demonstrate that overexpression of C-terminus of the nucleotide exchange factor Cdc25p stimulates GAL10 transcription in yeast strains carrying the contemporary deletion of both RAS genes. Moreover, the deletion of the chromosomal CDC25 gene provokes impaired growth on galactose based media in yeast strain lacking both RAS genes and adenylate cyclase (whose viability is assured by the presence of the Bcy1-11 allele). Surprisingly, reconstitution of the Ras-pathway inhibits GAL10-promoter activation. Activation of GAL10 gene promoter is indeed possible in the presence of Ras protein but only in strains with chromosomal deletion of adenylate cyclase. These results indicate a dual role of Ras-pathway on galactose metabolism and suggest that Cdc25p has a Ras-independent role in cellular metabolism.
在酿酒酵母中，当培养基中以半乳糖作为唯一碳源时，参与半乳糖代谢的基因（GAL1、7、10）的转录活性会被激活1000倍以上。在本研究中，我们监测了GAL10基因启动子在不同Ras-cAMP遗传背景下的活性。我们证明，在同时缺失两个RAS基因的酵母菌株中，核苷酸交换因子Cdc25p的C端过表达会刺激GAL10转录。此外，在缺乏两个RAS基因和腺苷酸环化酶（其生存能力由Bcy1-11等位基因的存在来保证）的酵母菌株中，染色体CDC25基因的缺失会导致在基于半乳糖的培养基上生长受损。令人惊讶的是，Ras途径的重建会抑制GAL10启动子的激活。事实上，在存在Ras蛋白的情况下，GAL10基因启动子的激活是可能的，但仅在染色体缺失腺苷酸环化酶的菌株中。这些结果表明Ras途径在半乳糖代谢中具有双重作用，并表明Cdc25p在细胞代谢中具有不依赖Ras的作用。
