Ste5 tethers multiple protein kinases in the MAP kinase cascade required for mating in S. cerevisiae.
Ste5 is a Zn2+ finger-like protein thought to function before three kinases, Ste11 (a MEKK), Ste7 (a MEK), and Fus3 (a MAPK), in a conserved MAP kinase cascade required for mating in S. cerevisiae. Here, we present evidence that Ste5 forms a multikinase complex that joins these kinases for efficient Fus3 activation. By two-hybrid analysis, Ste11, Ste7, and Fus3 associate with different domains of Ste5, while Kss1, another MAPK, associates with the same domain as Fus3, thus implying that Ste5 simultaneously binds a MEKK, MEK, and MAPK. Ste5 copurifies with Ste11, Fus3, and a hypophosphorylated form of Ste7, and all four proteins cosediment in a glycerol gradient as if in a large complex. Ste5 also increases the amount of Ste11 complexed to Ste7 and Fus3 and is required for Ste11 to function. These results substantiate a novel signal transduction component that physically links multiple kinases within a single cascade.
Choi
K Y
KY
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
Satterberg
B
B
Lyons
D M
DM
Elion
E A
EA
D048868:Adaptor Proteins, Signal Transducing; D001483:Base Sequence; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002352:Carrier Proteins; D004252:DNA Mutational Analysis; D005656:Fungal Proteins / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D046911:Macromolecular Substances; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D008954:Models, Biological; D008969:Molecular Sequence Data; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D012098:Reproduction; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D015398:Signal Transduction; D014157:Transcription Factors
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D005656:Fungal Proteins; D046911:Macromolecular Substances; C080321:STE5 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D014157:Transcription Factors; C071596:ste11 protein, S pombe; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C075580:FUS3 protein, S cerevisiae; C541984:KSS1 protein, S cerevisiae; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; C067018:Ste11 protein, S cerevisiae; D020929:Mitogen-Activated Protein Kinase Kinases