Protein kinase Byr2 is a target of Ras1 in the fission yeast Schizosaccharomyces pombe.
Conservation of the structure and function of Ras proteins has been observed in a variety of eukaryotic organisms. However, the nature of their downstream effectors appears to be quite divergent; adenylyl cyclase and a protein kinase Raf-1, which do not share any structural homology with each other, are effectors of Ras in the budding yeast and in higher organisms, respectively. We show here that a protein kinase Byr2, which has been known to act downstream of Ras1 in a mating pheromone signal transduction system of Schizosaccharomyces pombe, binds directly to Ras proteins in a GTP-dependent manner. The region of Byr2 responsible for the Ras binding was mapped by a gene deletion analysis to its N-terminal segment of 206 amino acid residues, which does not possess any significant homology with the other effectors of Ras. The affinity of the Byr2 N terminus for Saccharomyces cerevisiae Ras2 was determined by measuring its activity to competitively inhibit Ras-dependent adenylyl cyclase activity and found to be comparable with those of yeast adenylyl cyclase and human Raf-1, with a dissociation constant (Kd) of about 1 nM. Furthermore, Byr2 inhibited a Ras GTPase-activating activity of Ira2, a S. cerevisiae homologue of neurofibromin. These results indicate that Byr2 is an immediate downstream target of Ras1 in S. pombe.
Department of Physiology II, Kobe University School of Medicine, Japan.
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Masuda
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Kariya
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Shinkai
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Okada
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Kataoka
D000262:Adenylyl Cyclases / Q000378:metabolism; D004789:Enzyme Activation; D005656:Fungal Proteins / Q000378:metabolism / Q000502:physiology*; D020690:GTPase-Activating Proteins; D006160:Guanosine Triphosphate / Q000378:metabolism; D011494:Protein Kinases / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D029701:Saccharomyces cerevisiae Proteins; D012568:Schizosaccharomyces / Q000201:enzymology*; D029702:Schizosaccharomyces pombe Proteins; D020703:ras GTPase-Activating Proteins; D018631:ras Proteins
D005656:Fungal Proteins; D020690:GTPase-Activating Proteins; C064960:IRA2 protein, S cerevisiae; D011506:Proteins; D011518:Proto-Oncogene Proteins; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D020703:ras GTPase-Activating Proteins; D006160:Guanosine Triphosphate; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; C489014:RAS1 protein, S cerevisiae; C489015:RAS2 protein, S cerevisiae; C492657:Ras1 protein, S pombe; D018631:ras Proteins; D000262:Adenylyl Cyclases