Member of the two-component regulatory system EnvZ/OmpR involved in osmoregulation (particularly of genes ompF and ompC) as well as other genes (PubMed:2543631). EnvZ functions as a membrane-associated protein kinase that phosphorylates OmpR in response to environmental signals; at low osmolarity OmpR activates ompF transcription, while at high osmolarity it represses ompF and activates ompC transcription (Probable). ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Homodimer. Has several major domains; the N-terminal cytoplasmic domain is followed by 2 transmembrane helices that anchor the protein in the membrane; the periplasmic domain between the helices interacts with MrzA. The cytoplasmic C-terminal domain has a HAMP domain joined by a flexible linker to a histidine kinase domain. The HAMP domain by itself is intrinsically disordered. The cytoplasmic dimerization domain (CDD) forms an osmosensitive core and includes the autophosphorylated histidine residue. Autophosphorylated. Extended N-terminus.