The RNA chaperone Hfq, acting as a hexamer, is a known mediator of post-transcriptional regulation, expediting basepairing between small RNAs (sRNAs) and their target mRNAs. However, the intricate details associated with Hfq-RNA biogenesis are still unclear. Previously, we reported that the stringent response regulator, RelA, is a functional partner of Hfq that facilitates Hfq-mediated sRNA–mRNA regulation in vivo and induces Hfq hexamerization in vitro. Here we show that RelA-mediated Hfq hexamerization requires an initial binding of RNA, preferably sRNA to Hfq monomers. By interacting with a Shine–Dalgarno-like sequence (GGAG) in the sRNA, RelA stabilizes the initially unstable complex of RNA bound-Hfq monomer, enabling the attachment of more Hfq subunits to form a functional hexamer. Overall, our study showing that RNA binding to Hfq monomers is at the heart of RelA-mediated Hfq hexamerization, challenges the previous concept that only Hfq hexamers can bind RNA.
Bibliographical noteFunding Information:
We are grateful to Sarah Woodson for her advice throughout the study. We appreciate the excellent assistance in strain and plasmid construction by Tal Hershko-Shalev and Noa Nur. This work was supported by: the Israel Science Foundation founded by The Israel Academy of Sciences and Humanities (138/18), and the Deutsch-lsraelische Pro-jektkooperation (AM 441/1-1 SO 568/1-1).
© 2021, The Author(s).