Hfq binds directly to the ribosome- binding site of IS10 transposase mRNA to inhibit translation

Hfq is a critical component of post-transcriptional regulatory networks in most bacteria. It usually functions as a chaperone for base-pairing small RNAs, although non-canonical regulatory roles are continually emerging. We have previously shown that Hfq represses IS10/Tn10 transposase expression through both antisense RNA-dependent and independent mechanisms. In the current work, we set out to define the regulatory role of Hfq in the absence of the IS10 antisense RNA. We show here that an interaction between the distal surface of Hfq and the ribosome-binding site of transposase mRNA (RNA-IN) is required for repressing translation initiation. Additionally, this interaction was critical for the in vivo association of Hfq and RNA-IN. Finally, we present evidence that the small RNA ChiX activates transposase expression by titrating Hfq away from RNA-IN. The current results are considered in the broader context of Hfq biology and implications for Hfq titration by ChiX are discussed.