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, HlgC), Coa, DNase, Spa and cell wall-associated proteins (Emp, Eap, FnbA, FnbB, Efb). Represses the expression of type 5 capsular polysaccharide (cap operon). Also modulates the expression of several other genes. Phosphorylated by SaeS.