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. 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 (By similarity). Functions as a transcription regulator by direct binding to promoter regions of target genes (By similarity). Phosphorylated by SrrB.