Abstract
The mating mitogen-activated protein kinase (MAPK) cascade has three major outputs prior to fusion: transcriptional activation of many genes, cell cycle arrest in the G1 phase, and polarized growth. Bem1 localizes near the cortical actin cytoskeleton and is essential for polarized growth during mating. Here we show that Bem1 is required for efficient signal transduction and coordinates MAPK cascade activation with G1 arrest and mating. bem1delta null mutants are defective in G1 arrest and transcriptional activation in response to mating pheromone. Bem1 protein stimulates Fus3 (MAPK) activity and associates with Ste5, the tethering protein essential for activation of the MAPK kinase kinase Ste11. Bem1-Ste5 complexes also contain Ste11, Ste7 (MAPK kinase), and Fus3, suggesting that Ste5 localizes the MAPK cascade to Bem1. Strikingly, Bem1 also copurifies with Far1, a Fus3 substrate required for G1 arrest and proper polarized growth during mating. These and other results suggest that Bem1 may cross-link the Ste5-MAPK cascade complex to upstream activators and specific downstream substrates at the shmoo tip, thus enabling efficient circuitry for G1 arrest and mating.
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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Calcium-Calmodulin-Dependent Protein Kinases / metabolism*
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Carrier Proteins*
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Cell Cycle Proteins*
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Cell Cycle*
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Cyclin-Dependent Kinase Inhibitor Proteins
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Enzyme Activation
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Fungal Proteins / metabolism
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Fungal Proteins / physiology*
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GTP-Binding Proteins / physiology
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Intracellular Signaling Peptides and Proteins
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MAP Kinase Kinase Kinases / metabolism
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Mating Factor
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Mitogen-Activated Protein Kinases*
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Peptides / physiology
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Protein Binding
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Protein Serine-Threonine Kinases / physiology
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Repressor Proteins*
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Saccharomyces cerevisiae / cytology*
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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*
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Transcription, Genetic
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src Homology Domains
Substances
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Adaptor Proteins, Signal Transducing
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Carrier Proteins
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Cell Cycle Proteins
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Cyclin-Dependent Kinase Inhibitor Proteins
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FAR1 protein, S cerevisiae
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Fungal Proteins
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Intracellular Signaling Peptides and Proteins
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Peptides
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Repressor Proteins
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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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BEM1 protein, S cerevisiae
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Mating Factor
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Protein Serine-Threonine Kinases
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Calcium-Calmodulin-Dependent Protein Kinases
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FUS3 protein, S cerevisiae
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Mitogen-Activated Protein Kinases
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MAP Kinase Kinase Kinases
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STE20 protein, S cerevisiae
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Ste11 protein, S cerevisiae
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GTP-Binding Proteins