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Accessory gene regulator B The accessory gene regulator (agr) of Staphylococcus aureus is the central regulatory system that controls the gene expression for a large set of virulence factors. The arg locus consists of two transcripts: RNAII and RNAIII. RNAII encodes four genes (agrA, B, C, and D) whose gene products assemble a quorum sensing system. At low cell density, the agr genes are continuously expressed at basal levels. A signal molecule, autoinducing peptide (AIP), produced and secreted by the bacteria, accumulates outside of the cells. When the cell density increases and the AIP concentration reaches a threshold, it activates the agr response, i.e. activation of secreted protein gene expression and subsequent repression of cell wall-associated protein genes. AgrB and AgrD are essential for the production of the autoinducing peptide which functions as a signal for quorum sensing. AgrB is a transmembrane protein. AgrB is involved in the proteolytic processing of AgrD and may have both proteolytic enzyme activity and a transporter facilitating the export of the processed AgrD peptide. |
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