Structure of the Y14-magoh core of the Exon junction complex

Background: Splicing of pre-mRNA in eukaryotes imprints the resulting mRNA with a specific multiprotein complex, the exon-exon junction complex (EJC), at the sites of intron removal. The proteins of the EJC, Y14, Magoh, Aly/REF, RNPS1, Srm160, and Upf3, play critical roles in postsplicing processing, including nuclear export and cytoplasmic localization of the mRNA, and the nonsense-mediated mRNA decay (NMD) surveillance process. Y14 and Magoh are of particular interest because they remain associated with the mRNA in the same position after its export to the cytoplasm and require translation of the mRNA for removal. This tenacious, persistent, splicing-dependent, yet RNA sequence-independent, association suggests an important signaling function and must require distinct structural features for these proteins. Results: We describe the high-resolution structure and biochemical properties of the highly conserved human Y14 and Magoh proteins. Magoh has an unusual structure comprised of an extremely flat, six-stranded antiparallel beta sheet packed against two helices. Surprisingly, Magoh binds with high affinity to the RNP motif RNA binding domain (RBD) of Y14 and completely masks its RNA binding surface. Conclusions: The structure and properties of the Y14-Magoh complex suggest how the pre-mRNA splicing machinery might control the formation of a stable EJC-mRNA complex at splice junctions.