RNA-RNA Interactome Approaches Provide in vivo Evidence for a Critical Role of the Hfq Rim Face in sRNA-mRNA Pairing [RNA-seq]
Most bacterial small regulatory RNAs (sRNAs) modulate gene expression by forming complementary base pairs with target mRNAs, a process that is heavily reliant on the RNA chaperone Hfq in many microbes. Hfq, with its three distinct RNA-binding faces (proximal, rim, and distal), facilitates the simultaneous binding of sRNAs and target mRNAs, with each face providing specific interactions to promote pairing. However, the precise contributions of each Hfq face to RNA binding and sRNA-mRNA annealing in vivo remain unclear. Here, we systematically examined the functional impact of point mutations in chromomally-encoded Flag-tagged Hfq using the RNA Interaction by Ligation and Sequencing (RIL-seq) approach. While substantial numbers of sRNA-mRNA chimeras were detected for most Hfq face mutants, the rim face mutant R16A exhibited a near-complete loss of chimeras, even though functional assays confirmed that Hfq R16A retains partial regulatory activity. Further RIL-seq analysis demonstrated that the addition of the Flag tag did not significantly alter chimera formation or contribute to the loss of chimeras in R16A, and RNA immunoprecipitation sequencing (RIP-seq) analysis showed that R16A maintains partial RNA-binding activity. Using intracellular RIL-seq (iRIL-seq), a method with fewer in vitro processing steps after Hfq immunoprecipitation, we identified significantly more sRNA-mRNA chimeras in R16A compared to standard RIL-seq, indicating that the rim face plays a key role in stabilizing RNA pairs on Hfq. Our findings provide a comprehensive analysis of how the RNA-binding faces of Hfq contribute to sRNA stability and pairing in vivo and the unique function of the rim face. Additionally, we highlight the strengths of different RNA ligation-based sequencing approaches, with RIL-seq effectively capturing stable Hfq-associated interactions, while iRIL-seq captured more transient RNA pairings. Overall design: RNAseq profiling of Hfq mutants K31A, D9A, R16A and Y25D and corresponding wild-types.