TRANSCRIPTIONAL ANALYSIS OF DIFFERENT PROMOTERS IN THE SAR LOCUS IN STAPHYLOCOCCUS-AUREUS

The expression of extracellular virulence determinants in Staphylococc us aureus is controlled by a 510-nucleotide RNA molecule (RNAIII) whic h is a part of the agr system. The ngr operon, which encodes a multico mponent signal transduction system, is partially under the influence o f an unlinked regulatory locus called sar. The sar locus is composed o f three overlapping transcripts, designated sarA (0.56 kb), sarC (0.8 kb), and sarB (1.2 kb), originating from the P1, P3, and P2 promoters, respectively. In this study, we analyzed the differential expression of these promoters by using transcriptional fusion with the xylE repor ter gene to study the activation of the sar locus. The data confirm th e existence of three independent promoters with different promoter act ivities. Maximal promoter activity was observed with the combined fusi on of P-2-P-3-P-1 promoters. Expression studies with a sigB mutant rev ealed that the P3 promoter is SigB dependent. Analysis of these transc riptional fusions in a sarA mutant and in complemented strains with ea ch of the sar transcriptional units revealed that the snr locus is aut oregulatory, with SarA acting as a positive regulator, From various tr anscriptional fusion studies of the upstream region of the P1 promoter , we have localized a 34-bp sequence which seems to play a role in dow n-modulating P1 transcription. Using heparin-Sepharose and DNA-specifi c columns, we partially purified a 12-kDa protein, possibly a represso r, which binds to the promoter regions upstream of P2 and P1 and which also binds to the 34-bp sequence, These data indicated that the regul ation of the snr locus is complex and may involve the sar gene product (s) and other regulatory protein(s).