Research progress of Escherichia coli RNA chaperone Hfq interaction with DsrA and rpoS

Hfq is a bacterial post-transcriptional regulator. It facilitates base-pairing between sRNA and target mRNA. The mRNA rpoS, which encodes the master regulator σ^s of general stress response, requires Hfq-facilitated base pairing with DsrA small RNA for efficient translation at low temperatures. Two mutually non-exclusive mechanisms have been proposed to explain the process of how Hfq facilitates base pairing of sRNA DsrA to mRNA rpoS: Hfq may form ternary complex with two RNAs via co-binding to bring the RNA strands into close proximity for optimal annealing; Hfq may bind one or both RNAs, and change its (or their) secondary (or tertiary) structure to facilitate the RNA pairing. Recently, several complex crystal structures of AU ₆A-Hfq-ATP, A_ΓHfq, and AU₆A-Hfq-A ₇ were acquired, and interesting structural features were extracted from them to deepen our understanding in the RNA binding properties of Hfq and its RNA complexes. Furthermore, the formation of ternary complex sRNA-Hfq-mRNA is proved to be necessary for translation activation of rpoS mRNA in vivo. This mini-review summarizes some recent structural biology advances in the research of DsrA-regulated translation of rpoS and the biological implications of the transient ternary complex are discussed.