Member of the two-component regulatory system SrrA/SrrB, which is involved in the global regulation of staphylococcal virulence factors in response to environmental oxygen levels as well as biofilm formation (PubMed:24222487). Also plays an essential role in host-derived nitric oxide resistance by regulating hmp/flavohemoglobin, an enzyme that detoxifies nitric oxide by converting it to nitrate (PubMed:16859493, PubMed:24222487). Functions as a sensor protein kinase which is autophosphorylated at a histidine residue and transfers its phosphate group to SrrA. In turn, SrrA binds to the upstream promoter regions of the target genes to positively and negatively regulate their expression (Probable). ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Up-regulated during anaerobic growth. Inactivation significantly enhances staphylococcal nitric oxide susceptibility.