Roquin binding to target mRNAs involves a winged helix-turn-helix motif

Roquin proteins mediate mRNA deadenylation by recognizing a conserved class of stem-loop RNA degradation motifs via their Roquin domain. Here we present the crystal structure of a Roquin domain, revealing a mostly helical protein fold bearing a winged helix-turn-helix motif. By combining structural, biochemical and mutation analyses, we gain insight into the mode of RNA binding. We show that the winged helix-turn-helix motif is involved in the binding of constitutive decay elements-containing stem-loop mRNAs. Moreover, we provide biochemical evidence that Roquin proteins are additionally able to bind to duplex RNA and have the potential to be functional in different oligomeric states.