Member of the two-component regulatory system GraR/GraS involved in resistance against cationic antimicrobial peptides (CAMPs). GraS probably functions as a sensor protein kinase which is autophosphorylated at a histidine residue and transfers its phosphate group to GraR (By similarity). ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Autophosphorylated.