Member of the two-component regulatory system SaeR/SaeS involved in the regulation of staphylococcal virulence factors in a strain-dependent fashion. Probably functions as a membrane-associated protein kinase that upon sensing the appropriate signal, autophosphorylates and in turn activates the cytosolic response regulator SaeR. SaeR/SaeS activates the expression of exoproteins involved in adhesion and invasion of host cells, including hemolysins (hla, hlb), coa, Dnase, spa and cell wall-associated proteins (emp, eap, fnbA). Acts probably downstream of the agr system in the regulatory cascade of virulence factors. ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Expressed at high levels in the late and post-exponential growth phases. Transcription is affected by Agr and SarA. Also, transcriptionally repressed by NaCL, pH below 6, glucose and the antibiotic clindamycin. Autophosphorylated.