An RNA trap helps bacteria get the most out of chitosugars.

Small regulatory RNAs (sRNAs) are well known to command bacterial protein synthesis by modulating the translation and decay of target mRNAs. Most sRNAs are specifically regulated by a cognate transcription factor under certain growth or stress conditions. Investigations of the conserved Hfq-dependent MicM sRNA in Escherichia coli (article by Poul Valentin-Hansen and colleagues in this issue of Molecular Microbiology) and in Salmonella have unravelled a novel type of gene regulation in which the chitobiose operon mRNA acts as an RNA trap to degrade the constitutively expressed MicM sRNA, thereby alleviating MicM-mediated repression of the synthesis of the YbfM porin that is required for chitosugar uptake. The results suggest that 'target' mRNAs might be both prey and also predators of sRNAs.