Crystal structure of the Drosophila Mago nashi-Y14 complex.

Pre-mRNA splicing is essential for generating mature mRNA and is also important for subsequent mRNA export and quality control. The splicing history is imprinted on spliced mRNA through the deposition of a splicing-dependent multiprotein complex, the exon junction complex (EJC), at approximately 20 nucleotides upstream of exon-exon junctions. The EJC is a dynamic structure containing proteins functioning in the nuclear export and nonsense-mediated decay of spliced mRNAs. Mago nashi (Mago) and Y14 are core components of the EJC, and they form a stable heterodimer that strongly associates with spliced mRNA. Here we report a 1.85 A-resolution structure of the Drosophila Mago-Y14 complex. Surprisingly, the structure shows that the canonical RNA-binding surface of the Y14 RNA recognition motif (RRM) is involved in extensive protein-protein interactions with Mago. This unexpected finding provides important insights for understanding the molecular mechanisms of EJC assembly and RRM-mediated protein-protein interactions.