A broadening world of bacterial small RNAs

Abstract

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.

Figure 1. Different types of sRNAs based on their mechanism of action

Trans-encoded sRNAs can base-pair imperfectly with mRNA targets and either (A) repress or (B) activate translation. Alternatively, (C) some trans-encoded sRNAs interact with proteins, including transcription factors, and inhibit their activity. Cis-encoded antisense sRNAs can also either (D) activate or (E) repress protein expression. Colored arrows represent RNA transcripts; black boxes indicate Shine-Dalgarno (SD) sequences. Dashed colored arrows represent unstable transcripts. Dashed black arrows represent hypothetical mechanistic steps of sRNA-mediated regulatory pathways.