In Staphylococcus aureus, one QS system involves the
sRNA RNAIII, which plays an important role in virulence,
demonstrating the pivotal role a sRNA can play in diverse
parts of bacterial physiology. This micro-organism uses the
peptide RNAIII-activating protein (RAP) and its target
molecule TRAP as autoinducers, detected by two-component
associated membrane sensor kinases that phosphorylate
the cognate cytoplasmic response regulators (Lyon & Novick,
2004). At high cell density, binding of the autoinducing peptide triggers expression of the regulatory RNA RNAIII.
This RNAIII represses expression of genes encoding cell
adhesion proteins important for early colonization stages,
and induces expression of genes encoding several toxins,
exoproteins and other virulence factors (Johansson &
Cossart, 2003; Korem et al., 2005; Toledo-Arana et al.,
2007) (see ‘Role of sRNA in pathogenesis’ below).