Member of the two-component regulatory system DegS/DegU, which plays an important role in the transition growth phase. Involved in the control of expression of different cellular functions, including production of degradative enzymes such as the neutral and alkaline proteases, flagellum formation and biofilm formation. Acts as both a protein kinase that undergoes autophosphorylation and subsequently transfers the phosphate to DegU, and a protein phosphatase that dephosphorylates phospho-DegU. ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Regulated via serine phosphorylation of its input domain. Phosphotransfer from DegS to DegU is stimulated by phosphorylation on Ser-76 and by DegQ. Autophosphorylated. Phosphorylated in vitro at Ser-76 by the serine/threonine-protein kinase YbdM, which stimulates the phosphate transfer to DegU.