Identification and characterization of SarH1, a new global regulator of virulence gene expression in Staphylococcus aureus

Abstract

The global regulators agr (accessory gene regulator) and sarA (staphylococcal accessory regulator) have been reported to be both activators and repressors of virulence gene expression in Staphylococcus aureus. How the effector of the agr system, RNAIII, interacts with target gene promoters is unknown. SarA, on the other hand, is a DNA‐binding protein, which binds to conserved DNA motifs immediately upstream of both positively and negatively regulated promoters. Here, we searched for additional regulators that could explain the differential effects of RNAIII and SarA. Four differently regulated genes (hla, alpha‐toxin; hld, RNAIII; spa, protein A; ssp, serine protease) were analysed for binding of potential regulatory proteins to the corresponding promoter DNA fragments, linked to magnetic beads. One protein (29 kDa), with affinity for all four promoters, showed a high degree of similarity to SarA and was named SarH1 (Sar homologue 1). Expression of sarH1 was strongly repressed by sarA and agr. Analysis of hla, hld, ssp and spa mRNAs in sarH1, sarA and agr mutants, and in sarA/sarH1 and agr/sarH1 double mutants, revealed that sarH1 has a strong repressive effect on hla and an activating effect on spa transcription. SDS–PAGE analysis of secreted proteins from the different mutants showed that the production of several other exoproteins was affected by sarH1. In conclusion, we show that both the agr‐dependent suppression of protein A production and the sarA‐dependent stimulation of alpha‐toxin production is mediated via a new regulator, SarH1, which belongs to a family of Sar homologues.

Regulation and characterization of rot transcription in Staphylococcus aureus

“…Regulation of the sarA family of genes is intertwined in nature (Manna & Cheung, 2006a, b). It should be stressed that sarS is transcribed in the early growth phase and tapers off in transcription at the postexponential and stationary phases of growth in RN6390 strain Tegmark et al, 2000). In the future, we will be analysing various sarA family mutant strains of S. aureus from different genetic backgrounds to determine if there is any variability of the data presented in this report.…”

“…These results are consistent with our earlier finding that most of the SarA paralogues regulate each other. Furthermore, the SarA paralogues involved in virulence gene regulation are intertwined: for example, sarR represses SarA expression , sarA represses and rot activates sarS expression Said-Salim et al, 2003;Tegmark et al, 2000), sarA negatively regulates sarT and sarT activates sarS , both SarA and MgrA repress sarV (Manna et al, 2004), while MgrA activates sarX transcription (Manna & Cheung, 2006b). …”

“…SarA is the first characterized member of the SarA family; others characterized are SarR , SarS (also called SarH1) Tegmark et al, 2000), SarT , Rot (McNamara et al, 2000), SarU (Manna & Cheung, 2003), SarV (Manna et al, 2004), MgrA (Luong et al, 2003;Truong-Bolduc et al, 2003) and SarX (Manna & Cheung, 2006b). The SarA family represents a group of DNA-binding proteins that share homology with each other (20-45 % identity and 45-65 % similarity to SarA protein) as well as with the MarR family of proteins involved in regulating multi-drug resistance in Gram-negative bacteria (Cheung & Zhang, 2002).…”

The SarA protein family of Staphylococcus aureus

“…Within each winged helix motif is a helix-turn-helix motif (α3α4) and a β-hairpin turn wing (β2β3), both of which are putative DNA binding domains (Liu et al, 2006). SarS is a 250-residue DNA binding protein that activates protein A gene (spa) transcription (Table 1) (Tegmark et al, 2000;Cheung et al, 2004). Unlike the dimeric structures of SarA and SarR, SarS forms a monomeric structure with two homologous but non-identical halves (Fig.…”

“…SarS is a 250-residue two-domain SarA homolog that activates spa and represses hla transcription (Tegmark et al, 2000;Cheung et al, 2004)}. Transcriptional analysis indicated that sarS is repressed by agr and mgrA and activated by ClpXP protease (Frees et al, 2005).…”