The structure of the N-terminal domain of Nup214 reveals a sevenbladed beta-propeller fold followed by a 30-residue C-terminalextended peptide segment. The CTE folds back onto the beta propeller and binds to its bottom face. The structure of the Nup214 NTD bound to the helicase Ddx19 in its ADP-bound state reveals the molecular basis for the interaction between the two proteins. A conserved residue of Ddx19 is shown to be crucial for complex formationin vitro and in vivo. Strikingly, the interaction surfaces exhibit strongly opposing surface potentials, with the helicase surface being positively and the Nup214 surface being negatively charged. Ddx19 is shown to bind RNA only in its ATP-bound state, and the binding of RNA and the Nup214 NTD is mutually exclusive.