RNA-RNA interactomes of ProQ and Hfq reveal overlapping and competing roles

Base pairing RNAs modulate gene expression in all studied organisms. In many bacteria, the base pairing between most small regulatory RNAs (sRNAs) and their targets is mediated by the Hfq RNA chaperone. However, recent studies have shown FinO-domain proteins also bind sRNAs. To examine the global contribution of the FinO-domain ProQ protein in Escherichia coli, we carried out RIL-seq to identify RNA pairs bound to this protein. The RNA-RNA interactome for ProQ contains hundreds of pairs. Intriguingly, a significant fraction of the ProQ-bound RNA pairs also are found associated with Hfq, indicating overlapping, complementary or competing roles for the two proteins. Characterization of one novel RNA pair bound by both chaperones revealed that while Hfq is required for RNA sponge-mediated down regulation of the sRNA, ProQ can inhibit this regulation. Overall our results uncover increased complexity in RNA regulatory networks involving RNA chaperone proteins, RNases, sRNAs and mRNAs.