Member of the two-component regulatory system WalK/WalR that regulates genes involved in autolysis and cell wall metabolism. WalK functions as a sensor protein kinase which is autophosphorylated at a histidine residue and transfers its phosphate group to WalR. ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. ATPase activity is inhibited by derivatives of thiazolidinone, benzamide and furan in vitro. Autophosphorylated.