The two-component system SaeRS consisting of the histidin kinase SaeS and the response regulator SaeR is known to act on virulence gene expression in Staphylococcus aureus. In order to get a more comprehensive picture on SaeR-regulated genes, we studied the contribution of the two-component system on global gene expression by using both the proteomic and transcriptomic approach. Altogether, a loss of SaeRS resulted in a decreased amount of at least 17 extracellular proteins and two cell surface-associated proteins, among them several important virulence factors such as HlgA, HlgB, HlgC, LukF, and LukM. SaeRS activates the expression of these genes at the transcriptional level. The amount of the five proteins Aur, SspA, SsaA, Plc, and GlpQ was negatively influenced by SaeRS. However, the transcription of the corresponding genes was not affected by the two-component system. SaeRS had also no measurable influence on the transcription of the regulatory genes agr, sarA, arlRS, and sigB that contribute to the regulation of SaeRS-dependent virulence factors identified in this investigation. Our results clearly show that SaeRS is strongly involved in the tight temporal control of virulence factor expression in S. aureus. Its precise role within the regulatory network remains to be determined.Staphylococcus aureus is a gram-positive bacterium that colonizes the anterior nares of at least one-third of the human population but also causes a variety of infections ranging from superficial lesions, such as wound infections and abscesses, to severe systemic infections such as bacteremia, endocarditis, pneumonia, and osteomyelitis. The pathogenicity of this organism largely depends on the successful adaptation to the human host and the environmentally coordinated expression of virulence factors. The expression of virulence factors in S. aureus is regulated during the growth cycle by a network of interacting regulators (for a review, see reference 41). The best-characterized virulence-associated regulons thus far are the agr regulon (accessory gene regulator), the SarA regulon (staphylococcal accessory regulator), the B regulon (alternative sigma factor), the Rot regulon (regulator of toxins), and the ArlRS regulon (autolysis-regulated locus) (7,15,20,37,47,60,61).The sae locus was first described by Giraudo et al. (27) following the characterization of a Tn551 insertional mutant of S. aureus RC161. sae is a regulatory locus that consists of four open reading frames, two of them encode the response regulator and the sensor kinase, respectively (23). Two additional open reading frames coding for hypothetical proteins are probably important for the functionality of the sae operon (42, 56).