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 transcriptional regulator via a specific DNA-binding domain, recognizing motifs near the promoter sequences of target genes. 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. Expressed at high levels in the late and post-exponential growth phases. Autoregulated. Transcription is affected by Agr and SarA. Also, transcriptionally repressed by NaCL, pH below 6, glucose and the antibiotic clindamycin. Phosphorylated by SaeS.