Regulatory organization of the staphylococcal sae locus

Abstract

This paper describes an investigation of the complex internal regulatory circuitry of the staphylococcal sae locus and the impact of modifying this circuitry on the expression of external genes in the sae regulon. The sae locus contains four genes, the saeR and S two-component signalling module (TCS), and saeP and Q, two upstream genes of hitherto unknown function. It is expressed from two promoters, P A sae, which transcribes only the TCS, and P C sae, which transcribes the entire locus. A bursa aurealis (bursa) transposon insertion in saeP in a derivative of Staphylococcus aureus NCTC 8325 has a profound effect on sae function. It modifies the activity of the TCS, changing the expression of many genes in the sae regulon, even though transcription of the TCS (from P A sae) is not interrupted. Moreover, these effects are not due to disruption of saeP since an in-frame deletion in saeP has essentially no phenotype. The phenotype of S. aureus strain Newman is remarkably similar to that of the saeP : : bursa and this similarity is explained by an amino acid substitution in the Newman saeS gene that is predicted to modify profoundly the signalling function of the protein. This concurrence suggests that the saeP : : bursa insertion affects the signalling function of saeS, a suggestion that is supported by the ability of an saeQR clone, but not an saeR clone, to complement the effects of the saeP : : bursa insertion.

Differential regulation of staphylococcal virulence by the sensor kinase SaeS in response to neutrophil-derived stimuli

“…Future studies will elucidate exactly why this methionine is essential to the SaeS sensing domain. Because this kinase appears to be completely unable to activate transcription of sae target genes, suggesting it may be in in a "locked off" conformation, it would be informative to combine the M31A mutation with the constitutively active mutation L18P found in strain Newman (15,44,45). It should be noted that, although we predict M31 to be EC regardless of its exact localization, we identified a residue that is essential for signaling in a major virulence regulatory system in S. aureus.…”

“…5 and Tables S2 and S3). Due to autoregulation of the sae system from the P1 promoter, transcript levels of saeR and saeS increase moderately on activation of the system (13,15). An increase in expression of saeR was observed in all strains capable of activating sae-dependent gene expression (WT v, ΔsaeS-WT SaeS, W32A, F33A, and H36A; Tables S2 and S3).…”

“…However, formation of the protein complex results in repression of the sae system and not activation. In addition, saeP is not required for the sae system to activate (15). Therefore, how SaeS senses host signals known to activate the sae system is unclear.…”

“…SaeR is a member of the OmpR family of response regulators and binds a direct DNA repeat sequence upon phosphorylation by SaeS to activate transcription of genes in the sae regulon (11,14). SaeS, a member of the HisKA family of histidine protein kinases, is predicted to contain a sensing domain composed of only two transmembrane segments connected by a short extracellular loop (15). Work on the antimicrobial peptide sensing TCS ApsXRS in Staphylococcus epidermidis suggests the nine amino acid extracellular (EC) loop of the sensor kinase ApsS may be sufficient to detect the presence of specific host antimicrobial peptides.…”

Identification of the P3 Promoter and Distinct Roles of the Two Promoters of the SaeRS Two-Component System in Staphylococcus aureus

“…saeP and saeQ are predicted to produce a lipoprotein (146 amino acids [aa]) and a membrane protein (157 aa), respectively. However, the function of the proteins is unknown except for the fact that saePQ is dispensable for sae signaling (1,30). The genes saeR and saeS encode the RR and HK, respectively.…”