The ubiquity of small RNAs (sRNAs) in bacteria is now well established. These transcripts are the members of regulatory circuits involved in diverse processes ranging from stress adaptation to virulence to metabolism. Recent large-scale searches suggest that there exist many times more sRNAs than previously predicted even in the best studied bacterial transcriptomes. On the basis of these and other recent findings of regulatory sRNAs that do not function in a 'classical' manner, we propose that the working definition of sRNAs be broadened.
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