Eukaryotic Translation Initiation Factor 3J (EIF3J)

EIF3J promoted binding of a core subcomplex made up of EIF3B, EIF3G, and EIF3I. Purified EIF3 lacking EIF3J bound 40S ribosomal subunits weakly, but it bound tightly when EIF3J was added. Cleavage of a 16-residue C-terminal peptide from EIF3J by caspase-3 (CASP3) reduced its affinity for the 40S ribosomal subunit, and the cleaved form provided substantially less stabilization of purified EIF3-40S complexes. EIF3J bound directly to the mRNA entry channel and aminoacyl site of the 40S subunit, placing EIF3J directly in the ribosomal decoding center. EIF3J also interacted with EIF3A and reduced 40S subunit affinity for mRNA. High affinity for mRNA was restored upon recruitment of initiator tRNA, even though EIF3J remained in the mRNA-binding cleft in the presence of tRNA.