Eukaryotic initiation factor 4A (eIF4A) is a minimal (394 residues) DEAD-box RNA helicase. Its crystallographic structure reveals two domains which have similar core topology to the equivalent domains of DNA and viral RNA helicases.
In our crystals of full-length eIF4A, the molecule has a "dumbbell" conformation. We presume that it must condense into a compact structure in order to bind duplex RNA and dissociate the RNA strands. The structure provides a framework for further studies on the mechanism of RNA recognition and unwinding.
The "DbpA" family of prokaryotic RNA helicases, including the Bacillus subtilis YxiN protein, bind 23S ribosomal RNA with high affinity and specificity. They are modular, consisting of a minimal helicase fragment plus a small carboxy-terminal extension that is responsible for specific RNA binding. The carboxy-terminal RNA binding domain has an "RNA recognition motif" fold:
However, the domain appears to bind RNA in a manner that differs from that of eukaryotic RNA recognition motifs.