Theagr P2 operon: An autocatalytic sensory transduction system inStaphylococcus aureus

The synthesis of virulence factors and other exoproteins inStaphylococcus 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 byagr. Theagr locus consists of two divergent operons, transcribed from neighboring but non-overlapping promoters, P2 and P3. The P2 operon sequence, reported here, contains 4 open reading frames,agr A, C, D, andB, of whichA andC appear to encode proteins of a classical 2-component signal transduction pathway. The P3 operon specifies a 0.5 kb transcript, RNA III, which is the actual effector of theagr response, and, incidentally, encodes theagr-regulated peptide δ-hemolysin. Transcriptional fusions have shown that both P2 and P3 areagr sensitive (function in anagr+ but not in anagr background) and deletion analysis has shown that all four of the P2 ORFs are involved;agrA andagrC seem to be absolutely required for the transcriptional activation of theagr locus, whereasagrB andagrD seem to be partially required. Since transcription of P2 requires P2 operon products, the P2 operon is autocatalytic, and is thus admirably suited to the need for rapid production of exo-proteins at a time when overall growth is coming to a halt.