A model of the changes in PTC-containing mRNA-protein complexes (mRNPs) during nuclear export. A PTC-containing transcript, depicted as in Figure 1, is capped, spliced and polyadenylated. Concomitantly, the cap-binding complex (CBC, consisting of CBP80 and CBP20), the exon junction complex (EJC, which consists of the DEK, REF/Aly, RNPS1, SRm160 and Y14 proteins), the NMD protein hUpf3 and the export factor TAP/p15 are all added, to give a fully processed mRNP. Before or soon after export from the nucleus through the nuclear pore complex (NPC), DEK, RNPS1 and REF/Aly dissociate from the EJC and hUpf2 binds. It is not clear whether the first round of translation can be mediated by CBC (left) or whether CBC is first exchanged for eIF4E. After this first round, the PTC-containing mRNA undergoes nonsense-mediated decay. See text for further details. Figure modified from [23,26].