Serine/threonine protein kinase required for cell-type-specific transcription and signal transduction in yeast. It is thought that it is phosphorylated by the ste11 protein kinase and that it can phosphorylate the FUS3 and or KSS1 kinases. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Phosphorylated at multiple sites in response to pheromone. Present with 672 molecules/cell in log phase SD medium. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase subfamily.