Figure 5.

Model of substrate recruitment, phosphorylation and release by SMG-1–8–9. UPF1 is recruited to SMG-1 via the kinase domain and a binding site in the C-insertion domain. UPF1 binding induces a dislocation of the C-insertion from the kinase catalytic domain (red arrow). This rearrangement allows stable UPF1 binding and phosphorylation of N- and the C-terminal parts in the SMG-1 active site. UPF2 contacts SMG-1–8–9 next to the kinase catalytic domain via its MIF4G-3 domain (33) and facilitates release of phosphorylated UPF1.