Member of the two-component regulatory system CheAY/CheY that regulates chemotaxis and colonization of the gastric mucosa (PubMed:10722597). Functions as a sensor protein kinase which is autophosphorylated at a histidine residue and transfers its phosphate group to the conserved aspartic acid residue in the regulatory domain of CheY (PubMed:16207913). In turn, phosphorylated CheY (CheY-P) interacts with the flagellar motor protein FliM to cause clockwise flagellar rotation and bacterial reversals, as opposed to straight swimming when CheY is not phosphorylated (By similarity). ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Contains a C-terminal CheY-like regulatory domain where the phosphate can be transferred. Autophosphorylated. Mutants are unable to colonize mice.