Boy-Marcotte E, Ikonomi P, Jacquet M
Institut de Génétique et Microbiologie, URA Centre National de la Recherche Scientifique D1354, Université Paris XI, Orsay, France.
Mol Biol Cell. 1996 Apr;7(4):529-39. doi: 10.1091/mbc.7.4.529.
The SDC25 gene of Saccharomyces cerevisiae is homologous to CDC25. Its 3' domain encodes a guanine nucleotide exchange factor (GEF) for Ras. Nevertheless, the GEF encoded by CDC24 is determinant for the Ras/cAMP pathway activation in growth. We demonstrate that the SDC25 gene product is a functional GEF for Ras: the complete SDC25 gene functionally replaces CDC25 when overexpressed or when transcribed under CDC25 transcriptional control at the CDC25 locus. Chimeric proteins between Sdc25p and Cdc25p are also functional GEFs for Ras. We also show that the two genes are differentially regulated: SDC25 is not transcribed at a detectable level in growth conditions when glucose is the carbon source. It is transcribed at the end of growth when nutrients are depleted and in cells grown on nonfermentable carbon sources. In contrast, CDC25 accumulation is slightly reduced when glucose is replaced by a nonfermentable carbon source.
酿酒酵母的SDC25基因与CDC25同源。其3'结构域编码一种Ras的鸟嘌呤核苷酸交换因子（GEF）。然而，由CDC24编码的GEF对于生长过程中Ras/cAMP途径的激活起决定性作用。我们证明SDC25基因产物是一种功能性的Ras GEF：当在CDC25基因座处过表达或在CDC25转录控制下转录时，完整的SDC25基因在功能上可替代CDC25。Sdc25p和Cdc25p之间的嵌合蛋白也是功能性的Ras GEF。我们还表明这两个基因受到不同的调控：当以葡萄糖作为碳源时，在生长条件下SDC25不会转录到可检测水平。当营养物质耗尽时，在生长末期以及在以不可发酵碳源生长的细胞中，它会转录。相反，当用不可发酵碳源替代葡萄糖时，CDC25的积累会略有减少。
