Poly(A) polymerase is required for RyhB sRNA stability and function in .

Small regulatory RNAs (sRNAs) are an important class of bacterial post-transcriptional regulators that control numerous physiological processes, including stress responses. In Gram-negative bacteria including , the RNA chaperone Hfq binds many sRNAs and facilitates pairing to target transcripts, resulting in changes in mRNA transcription, translation, or stability. Here, we report that poly(A) polymerase (PAP I), which promotes RNA degradation by exoribonucleases through the addition of poly(A) tails, has a crucial role in the regulation of gene expression by Hfq-dependent sRNAs. Specifically, we show that deletion of , encoding PAP I, paradoxically resulted in an increased turnover of certain Hfq-dependent sRNAs, including RyhB. RyhB instability in the deletion strain was suppressed by mutations in or that disrupt pairing of RyhB with target RNAs, by mutations in the 3' external transcribed spacer of the transcript (3'ETS) involved in pairing with RyhB, or an internal deletion in , which encodes the endoribonuclease RNase E. Finally, the reduced stability of RyhB in the deletion strain resulted in impaired regulation of some of its target mRNAs, specifically and Altogether our data support a model where PAP I plays a critical role in ensuring the efficient decay of the 3'ETS In the absence of PAP I, the 3'ETS transcripts accumulate, bind Hfq, and pair with RyhB, resulting in its depletion via RNase E-mediated decay. This ultimately leads to a defect in RyhB function in a PAP I deficient strain.