Core component of the splicing-dependent multiprotein exon junction complex (EJC) deposited at splice junctions on mRNAs. The EJC is a dynamic structure consisting of core proteins and several peripheral nuclear and cytoplasmic associated factors that join the complex only transiently either during EJC assembly or during subsequent mRNA metabolism. The EJC marks the position of the exon-exon junction in the mature mRNA for the gene expression machinery and the core components remain bound to spliced mRNAs throughout all stages of mRNA metabolism thereby influencing downstream processes including nuclear mRNA export, subcellular mRNA localization, translation efficiency and nonsense-mediated mRNA decay (NMD). The MAGO-Y14 heterodimer inhibits the ATPase activity of EIF4A3, thereby trapping the ATP-bound EJC core onto spliced mRNA in a stable conformation. The MAGO-Y14 heterodimer interacts with the EJC key regulator PYM leading to EJC disassembly in the cytoplasm (By similarity). Can increase in vitro the expression from reporter constructs that contain leader introns required for the expression of different genes. In association with MAGO and PYM, participates in intron-mediated enhancement of gene expression (PubMed:21676911). The MAGO-Y14 heterodimer works synergistically with the NMD pathway to regulate male gametophyte development (PubMed:26867216). Heterodimer with Y14 (PubMed:19435936, PubMed:26867216). Part of the mRNA splicing-dependent exon junction complex (EJC); the core complex contains MLN51/CASC3, EIF4A3, MAGO and Y14 (Probable). Interacts with PYM (PubMed:16953428, PubMed:21676911). The interaction with PYM is direct and dissociates the EJC from spliced mRNAs (Probable). Interacts with EIF4A3 (PubMed:26867216). Nucleocytoplasmic shuttling protein. Travels to the cytoplasm as part of the exon junction complex (EJC) bound to mRNA. Expressed in root and shoot meristems, cotyledons, vascular tissues of leaves, receptacle of flowers and siliques, and pollen grains. Male sterility due to pollen abortion after meiosis. Belongs to the mago nashi family.