Molecular characterization of Ste20p, a potential mitogen-activated protein or extracellular signal-regulated kinase kinase (MEK) kinase kinase from Saccharomyces cerevisiae.

摘要: The Ste20p protein kinase was immunopurified from yeast cells and analyzed in an vitro assay system. immune complexes exhibited autophosphorylating activity at serine threonine residues specifically phosphorylated a bacterially expressed glutathione S-transferase (GST) fusion of Ste11p (a mitogen-activated or extracellular signal-regulated (MEK) homologue) residues. In contrast, GST fusions either Ste7p MEK the beta-subunit mating response G-protein immunoprecipitated Ste5p were not by complexes. Myelin basic identified as excellent substrate, whereas histone H1 only poorly phosphorylated. Evidence obtained that autophosphorylation might play regulatory role for activity. found to be Ca(2+)-independent. Both vivo activities abolished mutational changes conserved lysine residue 649 within ATP binding site 777 between catalytic subdomains VII VIII. Wild-type catalytically inactive T777A mutant phosphoproteins vivo. phosphorylation occurred independent pheromone stimulation. Based on genetically determined significance signal transduction our studies, we propose model represents whose function is link G-protein-coupled receptors through G beta gamma module.