Figure 2.

Model of the ABCE1 activity during translation initiation. We propose that the ABCE1, depicted in green, binds to either the 40S–deacylated tRNA–mRNA recycling intermediate along with eIFs 1, 1A and 3, which will then capture the ribosomal recycling stage by producing the free post-recycled 40S complex, or past this step directly to the post-recycled 40S-eIF1-eIF1A-eIF3 complex. During the pre-initiation and initiation stages ABCE1 may act as the critical anti-association factor by cycling on and off the ribosome in an NTP-dependent manner, unless its binding site at the GTPase binding region of the 40S subunit is occupied by other factors such as the eIF3b subunit. At a late initiation stage, eIF5B prevents ABCE1 from further cycling to promote proper subunit joining followed by GTP hydrolysis and its own release. Thick curved gray arrows indicate the eIF3b-g-i module relocation from the solvent to the intersubunit side of the 40S subunit. Red arrow indicates the conformational change of the eIF2-TC upon eIF3b relocation and departure to and from the intersubunit face of the 40S, which may reflect its described previously P^IN and P^OUT conformations. A question mark indicates an unknown fate of eIF3 that has been proposed to remain bound to the 40S subunit even past subunit joining PMID:18765792; PMID:18056426).