EIF3J

The crystal structure of the C-terminal part of human eIF3j was determined in the scope of the Structural Genomics Consortium and showed that it consists of a 6-helix bundle. eIF3j has subsequently been visualized as part of ribosomal translation initiation complexes, both for human and yeast eIF3j. The general binding location is similar for both species, located at the A-site between eIF1A and helix 16 of the ribosomal small subunit. However, differences are apparent in the arrangement of the C-terminal helix bundle and its rotation. The N-terminal part of eIF3j was visualized only in the context of a yeast pre-initiation complex, showing that it binds the entry of the mRNA tunnel.

Eukaryotic translation initiation factor 3 subunit J is reported to play an important role in the assembly of the 43S pre-initiation complex. It specifically binds to the 40S subunit in vitro and increases the affinity of eIF3 to the small subunit. The binding of eIF3j to the small subunit occurs in an anticooperative fashion with eIF1, eIF1A, and the ternary complex of eIF2, tRNA, and GTP. However, eIF3 reduces the negative cooperativity strongly.

eIF3j's N-terminal part binds the mRNA channel and has been shown to reduce the mRNA's affinity to the ribosomal small subunit, thus preventing translation initiation to progress. The ternary complex is essential to reduce eIF3j's affinity for the 43S pre-initiation complex and therefore to allow binding of mRNA. However, despite the presence of eIF3j, mRNA may still be able to bind in a pre-accommodated state in presence of eIF4A, meaning that the mRNA partially occupies the mRNA channel but is not in its final position.

Start codon selection is reported to be effected by eIF3j, as knock-out of eIF3j leads to less stringent selection of start codons

The activity of eIF3j may be regulated by phosphorylation by CK2 and through cleavage by caspase-3.