SAR GENETIC-DETERMINANTS NECESSARY FOR TRANSCRIPTION OF RNAII AND RNAIII IN THE AGR LOCUS OF STAPHYLOCOCCUS-AUREUS

The temporal expression of most virulence factors in Staphylococcus au reus is regulated by pleiotropic loci such as agr and sar. We have pre viously shown that the sar locus affects hemolysin production because it is required for agr transcription, To delineate the sar genetic det erminant required for agr transcription, single copies of fragments fr om the sar locus, encompassing the individual sar transcripts (sarA, s arC, and sarB), were introduced into a sar mutant via the integration vector pCL84. Although a DNA fragment encompassing the sarA transcript plus a 189-bp upstream region was sufficient for agr expression, comp lementation analysis revealed that the sarB transcript was the most ef fective in augmenting agr transcription as determined by RNAII and RNA III transcription and gel retardation assays with the P2 and P3 promot ers of agr. As the region upstream of the said transcript encodes a 39 -amino-acid open reading frame, ORF3, it is possible that posttranslat ional cooperation between the sarA gene product and ORF3 may be necess ary for optimal agr expression. Deletion studies demonstrated that an intact sarA gene is essential for agr transcription, However, mutagene sis and in vitro translation studies revealed that unlike the agr locu s, the required element is the SarA protein and not the RNA molecule, Taken together, these results indicate that the sarA-encoded protein, possibly in conjunction with peptides encoded in the upstream region, regulates hemolysin production by controlling agr P2 and P3 transcript ion.