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Summary

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.