The role of Rot in the regulatory cascade of Staphylococcus aureus virulence genes

Staphylococcus aureus produces a wide array of cell-surface and extracellular proteins involved in virulence. The expression of these virulence factors is tightly controlled by numerous regulators, including the well characterized S. aureus regulator (sar) and accessory gene regulator (agr). The effector of the sar response, the SarA protein, is a member of the Sar family of transcriptional regulators. SarA recognizes and binds to a consensus motif in the promoters of its target genes to control their expression. By yet, an unknown mechanism, the agr effector molecule, RNAIII, represses the expression of cell-surface proteins and activates the expression of secreted proteins.; Various studies by our laboratory and others have suggested the existence of co-factors that interact directly or indirectly with RNAIII to control the expression of S. aureus virulence genes. Potential candidates required for RNAIII activity include SarA homologues. Recently, a new SarA homologue was identified as a repressor of toxin (rot). Rot represses the production of α-toxin and protease, two significant determinants in S. aureus virulence.; Since most SarA homologues act as global regulators of virulence genes, we aimed to identify additional target genes whose expression is influenced by Rot. To address these questions, we analyzed the transcriptional profile of a rot/agr double mutant in comparison to its isogenic agr-null strain through the use of an Affymetrix GeneChip™. The custom-made Affymetrix GeneChip used in this study covers >86% of the S. aureus genome.; Our findings indicate that Rot is a modulator with both positive and negative effects on the expression of S. aureus genes. Included among these targets were two regulatory genes sarS and sigB. In addition our data showed that Rot and agr play opposite functions on certain target genes. These results provide further insight into the role of Rot in the regulatory cascade of S. aureus virulence gene expression as well as the interaction among Rot, agr, and sar.