Kinase involved in a signal transduction pathway that is activated by changes in the osmolarity of the extracellular environment. Seems to phosphorylate HOG1 on a tyrosine residue. 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] Interacts with NBP2, PTC1, SHO1 AND STE11. Alternative way of activation involves binding the proline-rich motif to the SH3 domain of SHO1. Activated by phosphorylation by SSK2 or SSK22. Ser/Thr phosphorylation is also necessary for SHO1-mediated activation. Present with 2160 molecules/cell in log phase SD medium. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase subfamily.