Abstract
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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adaptor Proteins, Signal Transducing*
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Base Sequence
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Calcium-Calmodulin-Dependent Protein Kinases / metabolism
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Carrier Proteins*
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DNA Mutational Analysis
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Fungal Proteins / metabolism*
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MAP Kinase Kinase Kinases / metabolism*
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Macromolecular Substances
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Mitogen-Activated Protein Kinase Kinases
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Mitogen-Activated Protein Kinases*
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Models, Biological
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Molecular Sequence Data
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Protein Binding
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Protein Kinases / metabolism*
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Reproduction
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Saccharomyces cerevisiae / metabolism*
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Saccharomyces cerevisiae Proteins*
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Schizosaccharomyces pombe Proteins*
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Signal Transduction*
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Transcription Factors*
Substances
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Adaptor Proteins, Signal Transducing
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Carrier Proteins
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Fungal Proteins
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Macromolecular Substances
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STE5 protein, S cerevisiae
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Saccharomyces cerevisiae Proteins
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Schizosaccharomyces pombe Proteins
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Transcription Factors
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ste11 protein, S pombe
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Protein Kinases
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Calcium-Calmodulin-Dependent Protein Kinases
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FUS3 protein, S cerevisiae
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KSS1 protein, S cerevisiae
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Mitogen-Activated Protein Kinases
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MAP Kinase Kinase Kinases
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Ste11 protein, S cerevisiae
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Mitogen-Activated Protein Kinase Kinases