title: Transcriptional regulation of a Ras nucleotide-exchange factor gene by extracellular signals in fission yeast.
abstract: 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.
authors.affiliation: Department of Biophysics and Biochemistry, School of Science, University of Tokyo, Japan.
authors.forename: D A
authors.initials: DA
authors.lastname: Hughes
authors.forename: N
authors.initials: N
authors.lastname: Yabana
authors.forename: M
authors.initials: M
authors.lastname: Yamamoto
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis* / Q000235:genetics; D015152:Blotting, Northern; D002454:Cell Differentiation; D005656:Fungal Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal / Q000235:genetics*; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D000072235:Mating Factor; D008957:Models, Genetic; D009584:Nitrogen / Q000172:deficiency; D010455:Peptides / Q000494:pharmacology; D010675:Pheromones / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012098:Reproduction; D012568:Schizosaccharomyces / Q000235:genetics* / Q000502:physiology; D029702:Schizosaccharomyces pombe Proteins; D015398:Signal Transduction / Q000235:genetics*; D014158:Transcription, Genetic; D018631:ras Proteins
chemical_list: D018528:ATP-Binding Cassette Transporters; D005656:Fungal Proteins; D020662:Guanine Nucleotide Exchange Factors; D010455:Peptides; D010675:Pheromones; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C489278:STE6 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins; D006153:Guanosine Diphosphate; D000072235:Mating Factor; D006160:Guanosine Triphosphate; C492657:Ras1 protein, S pombe; D018631:ras Proteins; D009584:Nitrogen