RNAIII activates map expression by forming an RNA-RNA complex in Staphylococcus aureus.

Staphylococcus aureus is a gram-positive pathogen responsible for a wide variety of diseases. RNAIII is the key effector of the accessory gene regulator (agr) system. It is a regulatory RNA (514 nucleotides long) that acts at both transcription and translation level to regulate the production of numerous toxins, enzymes and cell surface proteins. Here, we reveal that map (major histocompatibility complex class II analogous protein) is positively regulated by RNAIII. Our further study indicates that the 108-135nt fragment of RNAIII acts as an antisense RNA and anneals to map mRNA, forming RNA duplexes. The interaction between RNAIII and map mRNA may activate translation initiation. This may be helpful for understanding the regulation of virulence in S. aureus.