Mitogen-activated protein kinase involved in a signal transduction pathway that is activated by changes in the osmolarity of the extracellular environment (PubMed:7523111, PubMed:8662716, PubMed:8943326, PubMed:10198063, PubMed:10970855, PubMed:11230135, PubMed:11796711, PubMed:12743037, PubMed:14680476, PubMed:16321140, PubMed:16896207, PubMed:17363249, PubMed:17220467, PubMed:17346711). Controls osmotic regulation of transcription via the stress response element (STRE) in promoters of target genes (PubMed:7523111, PubMed:11336700). Upon osmotic shock, associates with the SKO1-SSN6-TUP1 complex, phosphorylates SKO1, and converts it into an activator that subsequently recruits Swi/Snf and SAGA complexes (PubMed:11230135, PubMed:12086627, PubMed:17429070). Activates the SMP1 transcription factor and the RCK2 kinase, both also involved in the regulation of the expression of a subset of osmotic stress-related genes (PubMed:10805732, PubMed:12482976). Phosphorylation of HSL1 by HOG1 leads to a G2 arrest essential for cell survival at high osmolarity (PubMed:16688223). Mediates also cell-cycle arrest in G1 phase by the dual targeting of SIC1 (PubMed:15448699). Regulates MFA2 ARE-mediated translation in response to carbon source (PubMed:16260593). Targets RPD3 histone deacetylase to osmoresponsive promoters to induce gene expression on stress (PubMed:14737171). Required for the Golgi apparatus localization of MNN1 (PubMed:9817752). Plays an essential role in maintaining water homeostasis, arsenite detoxification, copper-resistance, cold-resistance, hydrogen peroxide response, adaptation to citric acid stress, and repression of the mating pathway activity (PubMed:9744864, PubMed:11922108, PubMed:11136466, PubMed:15177185, PubMed:15060153, PubMed:15773992, PubMed:16920868, PubMed:16371351, PubMed:16790423, PubMed:16885417, PubMed:16857590). Functions as an arsenic sensor and effector via direct binding to arsenic and subsequent phosphorylation of the ARR1 transcription factor (PubMed:31772124). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by tyrosine and threonine phosphorylation (PubMed:9032256, PubMed:9211927, PubMed:11113180, PubMed:12455951, PubMed:12477803). Inactivated by dephosphorylation via recruitment of PTC1 to the PBS2-HOG1 complex after adaptation to osmotic stress (PubMed:14685261). PTP2 and PTP3 inactivate HOG1 by dephosphorylating Tyr-176, while the PP2Cs PTC1 and PTC2 or PTC3 dephosphorylate Thr-174 in the activation loop (PubMed:9032256, PubMed:9211927, PubMed:11113180, PubMed:12455951, PubMed:12477803). Interacts with CDC37, HOT1, KIN28, PTP2, PTP3, RBP1, RCK2, RPD3, SIC1, SMP1 and SIN4. Predominantly cytoplasmic in unstressed cells but rapidly concentrates within the nucleus in response to hyperosmotic conditions and phosphorylation. Arsenic-binding promotes the nuclear localization (PubMed:31772124). By osmotic stress, cold stress, citric acid, and in presence of bacterial lipopolysaccharides (LPS). The TXY motif contains the threonine and tyrosine residues whose phosphorylation activates the MAP kinases. Dually phosphorylated on Thr-174 and Tyr-176, which activates the enzyme. Leads to sensitivity to osmotic stress. Present with 6780 molecules/cell in log phase SD medium. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. MAP kinase subfamily. HOG1 sub-subfamily.