title: Homologous activators of ras in fission and budding yeast.
abstract: The ras proto-oncogene products are plasma membrane-bound, guanine nucleotide-binding proteins implicated in signal transduction across the plasma membrane. But the signal(s) that activates the ras pathway(s) is not known. In the budding yeast Saccharomyces cerevisiae, the CDC25 gene product acts upstream of Ras proteins, but it has not been clear whether CDC25 function is unique to the S. cerevisiae ras pathway. Here we report that the ste6 gene of fission yeast Schizosaccharomyces pombe is a homologue of CDC25: the ste6 gene product and the CDC25 gene product have significant amino-acid similarity in their C-terminal regions. Like the S. pombe ras1 gene, ste6 is essential for mating. Epistatic interactions indicate that the ste6 gene functions upstream of ras1. We propose that ste6 and CDC25 activate Ras protein through a common mechanism, perhaps by promoting GDP-GTP exchange, even though it seems that the function of Ras protein in budding yeast differs from that in fission yeast. Homologues of ste6 and CDC25 could regulate ras activity in other eukaryotic cells.
authors.affiliation: Institute of Medical Science, University of Tokyo, Japan.
authors.forename: D A
authors.initials: DA
authors.lastname: Hughes
authors.forename: Y
authors.initials: Y
authors.lastname: Fukui
authors.forename: M
authors.initials: M
authors.lastname: Yamamoto
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000595:Amino Acid Sequence; D001483:Base Sequence; D002453:Cell Cycle; D003001:Cloning, Molecular; D004271:DNA, Fungal / Q000235:genetics; D004843:Epistasis, Genetic; D005656:Fungal Proteins / Q000235:genetics*; D019204:GTP-Binding Proteins / Q000502:physiology*; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D006023:Glycoproteins; D020662:Guanine Nucleotide Exchange Factors; D008969:Molecular Sequence Data; D015689:Oncogene Protein p21(ras) / Q000502:physiology*; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D004718:Saccharomycetales / Q000235:genetics*; D012568:Schizosaccharomyces / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins
chemical_list: D018528:ATP-Binding Cassette Transporters; D004271:DNA, Fungal; D005656:Fungal Proteins; D006023:Glycoproteins; D020662:Guanine Nucleotide Exchange Factors; C489277:STE6 protein, S cerevisiae; C489278:STE6 protein, S pombe; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D019204:GTP-Binding Proteins; D015689:Oncogene Protein p21(ras)