SYNTHESIS OF STAPHYLOCOCCAL VIRULENCE FACTORS IS CONTROLLED BY A REGULATORY RNA MOLECULE

The production of most toxins and other exoproteins in Staphylococcus aureus is controlled globally by a complex polycistronic regulatory lo cus, agr. Secretory proteins are up-regulated by agr whereas surface p roteins are down-regulated. agr contains two divergent promoters, one of which directs the synthesis of a 514 nucleotide (nt) transcript, RN AIII. In this report, we show that the cloned RNAIII determinant resto res both positive and negative regulatory functions of agr to an agr-n ull strain and that the RNA itself, rather than any protein, is the ef fector molecule. RNAIII acts primarily on the initiation of transcript ion and, secondarily in some cases, at the level of translation. In th ese cases, translation and transcription are regulated independently. RNAIII probably regulates translation directly by interacting with tar get gene transcripts and transcription indirectly by means of intermed iary protein factors.