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.
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Gene/Complex | Qualifier | Gene Ontology Term | Annotation Extension | Evidence | Source | Assigned On |
---|---|---|---|---|---|---|
STE5 | involved in | pheromone-dependent signal transduction involved in conjugation with cellular fusion | IDA | SGD | 2013-08-07 | |
STE5 | enables | MAP-kinase scaffold activity | IDA | SGD | 2018-06-04 |
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Evidence ID | Analyze ID | Interactor | Interactor Systematic Name | Interactor | Interactor Systematic Name | Allele | Assay | Annotation | Action | Phenotype | SGA score | P-value | Source | Reference | Note |
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Interactor | Interactor | Assay | Annotation | Action | Modification | |
---|---|---|---|---|---|---|
FUS3 | STE5 | Two-hybrid | manually curated | Hit-Bait | No Modification | |
FUS3 | STE11 | Co-fractionation | manually curated | Hit-Bait | No Modification | |
STE5 | KSS1 | Two-hybrid | manually curated | Bait-Hit | No Modification | |
STE5 | STE11 | Two-hybrid | manually curated | Bait-Hit | No Modification | |
STE5 | STE11 | Co-fractionation | manually curated | Hit-Bait | No Modification | |
STE7 | STE5 | Two-hybrid | manually curated | Hit-Bait | No Modification |