Qrr

Qrr refers most commonly to a family of quorum regulatory RNAs (Qrr sRNAs) that regulate quorum sensing in Vibrio species. The Qrrs (often Qrr1–Qrr4 in many strains) are typically around 150–200 nucleotides long and rely on the RNA chaperone Hfq to function. They are part of the LuxO-controlled, autoinducer–responsive regulatory cascade that operates at low cell density.

Mechanism and targets: Qrr sRNAs base-pair with target mRNAs to modulate translation and stability. Notable targets include hapR in Vibrio cholerae and AphA in related Vibrio species; through these interactions, Qrr RNAs influence expression of traits such as bioluminescence, virulence factor production, and biofilm formation, enabling the bacteria to adjust gene expression programs as cell density changes.

Regulation: Qrr sRNA levels are driven by LuxO phosphorylation status, which is connected to autoinducer signals AI-1 and AI-2. At low cell density, LuxO is phosphorylated, promoting Qrr transcription; at high density, autoinducers activate phosphatases that reduce LuxO activity, decreasing Qrr levels and allowing HapR (and other high-density regulators) to accumulate. Qrrs thus implement a switch between cellular states in response to population density.

Other uses: As an acronym, Qrr can appear in different contexts outside bacterial quorum sensing, with definitions varying by field. In biology, the quorum regulatory RNA meaning is the best established usage.