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 transcription regulator by direct binding to promoter regions of target genes (By similarity). Up-regulated during anaerobic growth. Phosphorylated by SrrB. Inactivation significantly enhances staphylococcal nitric oxide susceptibility.