Two sRNA RyhB homologs from Yersinia pestis biovar microtus expressed in vivo have differential Hfq-dependent stability

Small non-coding RNAs (sRNAs) have been shown to modulate gene expression at the post-transcriptional level. RyhB, an iron-responsive sRNA, is conserved in Escherichia coli and other Enterobacteriae, indicating the downregulation of numerous genes during iron depletion. This sRNA is tightly regulated by the ferric uptake regulator (Fur) and interacts with the RNA binding protein Hfq. Hfq is generally purported to be essential for stabilizing sRNAs and promoting sRNA-mRNA duplex formation. Maintenance of iron homeostasis is an essential step in the lifecycle of Yersinia pestis. Y. pestis encodes two RyhB homologs, RyhB1 and RyhB2. In this study, we found that as in the case of E. coli, both RyhB homologs in Y. pestis are negatively regulated by Fur and have a half-life of >30 min. In the absence of Hfq, RyhB1 is rapidly degraded, while RyhB2 retains its stability. RyhB1 stabilization is mediated by Hfq, but RyhB2 does not require Hfq for stability. Additionally, both RyhBs are upregulated in lungs infected with Y. pestis, while the ryhB mutant shows no visible effects on virulence in mice upon either subcutaneous or intranasal inoculation. Collectively, our results indicate that the two RyhB homologs have common regulatory features in Y. pestis-infected lungs and in vitro, but that stability of RyhB1 and RyhB2 is differentially dependent on Hfq.