THE AGR P2 OPERON - AN AUTOCATALYTIC SENSORY TRANSDUCTION SYSTEM IN STAPHYLOCOCCUS-AUREUS

The synthesis of virulence factors and other exoproteins in Staphyloco ccus aureus is controlled by the global regulator, agr. Expression of secreted proteins is up-regulated in the postexponential growth phase, whereas expression of surface proteins is down-regulated by agr. The agr locus consists of two divergent operons, transcribed from neighbor ing but non-overlapping promoters, P2 and P3. The P2 operon sequence, reported here, contains 4 open reading frames, agr A, C, D, and B, of which A and C appear to encode proteins of a classical 2-component sig nal transduction pathway. The P3 operon specifies a 0.5 kb transcript, RNA III, which is the actual effector of the agr response, and, incid entally, encodes the agr-regulated peptide delta-hemolysin. Transcript ional fusions have shown that both P2 and P3 are agr sensitive (functi on in an agr(+) but not in an agr(-) back-ground) and deletion analysi s has shown that all four of the P2 ORFs are involved; agrA and agrC s eem to be absolutely required for the transcriptional activation of th e agr locus, whereas agrB and agrD seem to be partially required. Sinc e transcription of P2 requires P2 operon products, the P2 operon is au tocatalytic, and is thus admirably suited to the need for rapid produc tion of exoproteins at a time when overall growth is coming to a halt.