This family consists of several AgrD proteins from many Staphylococcus species. The agr locus was initially described in Staphylococcus aureus as an element controlling the production of exoproteins implicated in virulence. Its pattern of action has been shown to be complex, upregulating certain extracellular toxins and enzymes expressed post-exponentially and repressing some exponential-phase surface components. AgrD encodes the precursor of the autoinducing peptide (AIP).The AIP derived from AgrD by the action of AgrB interacts with AgrC in the membrane to activate AgrA, which upregulates transcription both from promoter P2, amplifying the response, and from P3, initiating the production of a novel effector: RNAIII. In S. aureus, delta-hemolysin is the only translation product of RNA III and is not involved in the regulatory functions of the transcript, which is therefore the primary agent for modulating the expression of other operons controlled by agr.