Involved in nonsense-mediated decay (NMD) of mRNAs containing premature stop codons by associating with the nuclear exon junction complex (EJC) and serving as link between the EJC core and NMD machinery. Recruits UPF2 at the cytoplasmic side of the nuclear envelope and the subsequent formation of an UPF1-UPF2-UPF3 surveillance complex (including UPF1 bound to release factors at the stalled ribosome) is believed to activate NMD. Binds spliced mRNA upstream of exon-exon junctions (By similarity). Shuttling between the nucleus and the cytoplasm. Expressed during early cleavage, gastrulation and at 1 day post-fertilization. Morpholino knockdown results in a weakly abnormal brain patterning during development that does not affect embryo viability at 5 days post-fertilization. Belongs to the RENT3 family. Contaminating sequence. Potential poly-A sequence.