TRANSCRIPTIONAL CONTROL OF THE AGR-DEPENDENT VIRULENCE GENE REGULATOR, RNAIII, IN STAPHYLOCOCCUS-AUREUS

Many of the genes coding for extracellular toxins, enzymes and cell-su rface proteins in Staphylococcus aureus are regulated by a 510 nt RNA molecule, RNAIII. Expression of the RNAIII gene is positively controll ed by the closely linked agr operon, which encodes a multicomponent si gnal-transduction system, and by an unlinked operon called sar. We hav e analysed the 120 bp region that separates the RNAIII promoter, P3, f rom the divergent agr promoter, P2. By transcription analysis, it was shown that P3 can function in trans of the agr operon, A stretch of 53 bp upstream of P3, containing an interrupted repeat of 7 bp, was foun d to be required for the agr-dependent expression of RNAIII, A single cytoplasmic protein was shown to bind to at least two sites within thi s regulatory region, The protein, which was absent in extracts from a sarA mutant, was identified as the sarA product by N-terminal amino ac id sequencing. A DNA fragment from the P2 region, encompassing an almo st identical repeated DNA motif, competed for the same protein. No int eraction between the regulatory DNA sequence and any agr-dependent pro ducts could be demonstrated. The results of this study suggest that P3 and P2 are controlled by a mechanism involving the binding of the Sar A protein to multiple sites within the regulatory regions immediately upstream of each promoter, and the as yet unknown activity of AgrA.