Magoh, a human homolog of Drosophila mago nashi protein, is a component ofthe splicing-dependent exon-exon junction complex

The RNA-binding protein Y14 binds preferentially to mRNAs produced by splic ing and is a component of a multiprotein complex that assembles similar to 20 nucleotides upstream of exon-exon junctions. This complex probably has i mportant functions in post-splicing events including nuclear export and non sense-mediated decay of mRNA. We show that Y14 binds to two previously repo rted components, Aly/REF and RNPS1, and to the mRNA export factor TAP. More over, we identified magoh, a human homolog of the Drosophila mago nashi gen e product, as a novel component of the complex. Magoh binds avidly and dire ctly to Y14 and TAP, but not to other known components of the complex, and is found in Y14-containing mRNPs in vivo. Importantly, magoh also binds to mRNAs produced by splicing upstream (similar to 20 nucleotides) of exon-exo n junctions and its binding to mRNA persists after export. These experiment s thus reveal specific protein-protein interactions among the proteins of t he splicing-dependent mRNP complex and suggest an important role for the hi ghly evolutionarily conserved magoh protein in this complex.