SarT Influences sarS Expression in Staphylococcus aureus

Abstract

Staphylococcus aureus is a gram-positive pathogen that is capable of expressing a variety of virulence proteins in response to environmental signals. Virulence protein expression in S. aureus is controlled by a network of regulatory loci including sarA and agr. The sarA/agr network is associated with the expression of cell wallassociated adhesins during exponential growth and the expression of secreted enzymes and toxins in the transition to post-exponential growth. A number of sarA homologs, including sarT and sarS, have been identified in the S. aureus genome. Previous studies have shown that sarA influences expression of both sarT and sarS in the global regulatory network. SarS has been shown to bind to the spa promoter to induce expression of protein A. SarT, one of the SarA homologs that represses hla expression and is repressible by SarA and agr, was found to induce sarS expression in this report. Northern blot analysis of sarS and spa expression in S. aureus RN6390, and the isogenic sarT, sarT sarA, and sarT agr mutants showed that while sarA regulated spa expression directly, the agr locus used sarT as an intermediary to regulate sarS, thus leading to spa repression in agr-activated cells. Gel shift and footprinting analysis showed that SarT binds to the sarS promoter, indicating that the interaction of the sarT gene product with the upstream region of sarS is likely direct. Induction of sarS and spa by SarT in agr ؉ strains was confirmed by a tetracycline-inducible system to titrate sarT expression.

Transcriptional profiling of a Staphylococcus aureus clinical isolate and its isogenic agr and sarA mutants reveals global differences in comparison to the laboratory strain RN6390

“…3). Although sarT has been reported to induce expression of sarS (Schmidt et al, 2003), the observation that sarS was expressed at lower levels in the sarT-positive strain RN6390, and higher levels in sarTnegative strains (UAMS-1, UAMS-601, UAMS-1138 and EMRSA-16) (Cassat et al, 2005), suggests that sarT may not be a primary determinant of the overall expression level of sarS in clinical isolates.…”

Reduced Vancomycin Susceptibility inStaphylococcus aureus, Including Vancomycin-Intermediate and Heterogeneous Vancomycin-Intermediate Strains: Resistance Mechanisms, Laboratory Detection, and Clinical Implications

“…Perhaps the most consistent transcriptional change observed for VISA strains is the downregulation of the spa gene (74,122,169,199,201,251,303). A possibly incomplete list of genes where the gene product has been shown to affect the transcription of spa includes agr (76,343), sarA (51,76,343), sarS (50), arlSR (85,86), sarT (304), srrAB (262), tcaR (200), mgrA (138), rot (240), ccpA (307), and sarZ (342). Potentially, a mutation in any of these regulatory genes could simultaneously increase vancomycin resistance and decrease protein A production.…”

Regulatory Elements of theStaphylococcus aureusProtein A (Spa) Promoter

“…SarS was shown to be a DNA binding protein and, thus, may up-regulate spa expression by direct binding to the spa promoter. Another member of the Sar family of proteins, SarT, has been shown to be a positive regulator of SarS (38). SarT was shown to bind to the sarS promoter.…”

“…A model has been proposed to explain the regulated expression of spa (38). In this model, the SarA protein binds to the spa promoter to repress transcription.…”

“…SarT was shown to bind to the sarS promoter. Expression of sarT results in sarS, and subsequently spa, expression (38).…”