The MAP kinase Fus3 associates with and phosphorylates the upstream signaling component Ste5.
Activation of the Saccharomyces cerevisiae MAP kinase Fus3 is thought to occur via a linear pathway involving the sequential action of three proteins: Ste5, a protein of unknown function, Ste11, a MAPKK kinase homolog, and Ste7, a MAPK kinase homolog which phosphorylates and activates Fus3. In this report, we present evidence for a novel mechanism of Fus3 activation that involves a direct association with Ste5, a protein not predicted to interact with Fus3. First, overexpression of Ste5 suppresses fus3 point mutations in an allele-specific manner and increases Fus3 kinase activity in vitro. Second, Ste5 associates with Fus3 in vivo as demonstrated by the two-hybrid system and by two methods of copurification. Third, Ste5 and Fus3 associate prior to pheromone stimulation even when Fus3 is inactive, and in strains lacking Ste7 and Ste11. Fourth Ste5 is phosphorylated by Fus3 in purified complexes and copurifies with an additional protein kinase(s). These observations suggest the possibility that Ste5 promotes signal transduction by tethering Fus3 to its activating protein kinase(s).
Kranz
J E
JE
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
Satterberg
B
B
Elion
E A
EA
D048868:Adaptor Proteins, Signal Transducing; D000483:Alleles; D002352:Carrier Proteins; D004789:Enzyme Activation; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal / Q000235:genetics*; D016153:Genes, Suppressor; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D010675:Pheromones / Q000378:metabolism; D010766:Phosphorylation; D017354:Point Mutation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D015398:Signal Transduction / Q000235:genetics*; D013489:Suppression, Genetic; D014157:Transcription Factors; D015854:Up-Regulation
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D005656:Fungal Proteins; D010675:Pheromones; C080321:STE5 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D014157:Transcription Factors; C071596:ste11 protein, S pombe; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; C075580:FUS3 protein, S cerevisiae; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; C067018:Ste11 protein, S cerevisiae; D020929:Mitogen-Activated Protein Kinase Kinases