Mitogen-activated protein kinase involved in a signal transduction pathway that is activated by changes in the osmolarity of the extracellular environment. Controls osmotic regulation of transcription of target genes. Involved in osmoregulation and stress response pathways leading to an efficient start of sexual differentiation. Supports translation initiation and facilitates adaptation to environmental stress in part through reducing eIF2-alpha phosphorylation. Links the cell-cycle G2/M control with changes in the extracellular environment that affect cell physiology. Phosphorylates atf1 and mkp1. In conjunction with hal4, has a role in the cellular resistance to toxic cations such as Na(+), Li(+) and Ca(2+). Involved in resistance to arsenite, methylglyoxal and hydrogen peroxide. Involved in induction of thermotolerance in mRNA export, as well as in vacuolar fission. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by the MAPK kinase wisl, and negatively regulated by pypl and pyp2 tyrosine phosphatases. Interacts with cdc37, cmk2, hal4, sin1 and srk1. Predominantly cytoplasmic in unstressed cells but rapidly concentrates within the nucleus in response to hyperosmotic conditions and phosphorylation. The TXY motif contains the threonine and tyrosine residues whose phosphorylation activates the MAP kinases. Dually phosphorylated on Thr-171 and Tyr-173, which activates the enzyme (By similarity). Phosphorylated by wis1 in response to osmotic stress, nutrient limitation, hydrogen peroxide and arsenite. Dephosphorylated by pyp1 and pyp2. Sensitive to methyl methanesulfonate (MMS, causes DNA breaks), hydroxyurea (HU, ribonucleotide reductase inhibitor), thiabendazole (TBZ), sirolimus (TORC1 inhibitor), and cold. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. MAP kinase subfamily. HOG1 sub-subfamily.