Ordered assembly of the EJC by the spliceosome.

(A) Assembly pathway of the EJC. For details, see Discussion. (B) The exon junction complex recruits NMD activating proteins and combines different complexes leading to UPF1-dependent NMD. The model of the BTZ-dependent pathway is derived from the data presented in this work, whereas the model of the UPF3b-UPF2-UPF1-dependent pathway is derived from collective data of earlier publications [34],[35],[39],[49]. Details are explained in the Discussion.