RNAIII is a stable 514 nt regulatory RNA transcribed by the P3 promoter of the Staphylococcus aureus quorum-sensing agr system ). It is the major effector of the agr regulon, which controls the expression of many S. aureus genes encoding exoproteins and cell wall associated proteins plus others encoding regulatory proteins  The RNAIII transcript also encodes the 26 amino acid δ-haemolysin (Staphylococcus aureus delta toxin) peptide (Hld). RNAIII contains many stem loops, most of which match the Shine-Dalgarno sequence involved in translation initiation of the regulated genes.
In the context of Staphylococcus aureus gene regulation, RNAIII is a crucial 514 nt regulatory RNA transcribed by the P3 promoter of the agr system. It controls the expression of numerous genes encoding exoproteins and cell wall-associated proteins, as well as those encoding regulatory proteins. The RNAIII transcript also encodes δ-haemolysin (Hld), a peptide involved in bacterial pathogenesis.