Forms part of a two-component regulatory system GacA/GacS(LemA). May be involved in lesion formation, swarming and in the production of extracellular protease, syringomycin and N-acyl-L-homoserine lactone (acyl-HSL). Required for pathogenicity on bean. ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Activation requires a sequential transfer of a phosphate group from a His in the primary transmitter domain, to an Asp in the receiver domain and to a His in the secondary transmitter domain.