Interesting twists on small RNA themes in Pseudomonas aeruginosa

While many of the initial studies of regulatory small RNA (sRNA) function focused on Escherichia coli and Salmonella, there is expanding characterization of sRNAs in other bacteria. These studies are revealing unique permutations of the themes found in E. coli and Salmonella. This point is nicely illustrated by the Pseudomonas aeruginosa Hfq-binding RNA, PhrS, which activates the synthesis of the key quorum sensing transcription regulator PqsR as described by Sonnleitner et al. in the current issue of Molecular Microbiology. The PhrS RNA combines features of several previously characterized sRNAs; its expression is induced by low oxygen, it encodes a small protein, and it modulates the expression of a quorum sensing regulator by preventing the formation of an inhibitory secondary structure. However, in contrast to other base pairing sRNAs that activate translation, PhrS does not act directly on pqsR but rather increases the translation of a small upstream open reading frame (uof) whose translation is coupled to pqsR.