Further biochemical characterization of rabbit reticulocyte eIF-4B.

In this report, it is shown that eIF-4B exhibits ATP hydrolysis activity in a ribosome-dependent fashion. This activity is significantly enhanced by the addition of eIF-4A and eIF-4F, although neither of these factors, alone or together, display a significant ribosome-dependent ATPase activity. Sepharose-6B gel filtration experiments with combinations of nonlabeled and 14C reductively methylated initiation factors (eIF-4A, eIF-4B, eIF-4F, and eIF-3) provide evidence that both eIF-4B and eIF-4F, but not eIF-4A, interact with ribosomes in the presence of specific factors and ATP. It is not known with which ribosomal subunit(s) these factors interact. In ultraviolet radiation-induced crosslinking studies, an eIF-4A and/or eIF-4F and ATP-dependent crosslinking of eIF-4B to radiolabeled oligo(A)12-18 was observed. Past studies with oxidized-cap mRNA achieved cross-linking of all three of these factors, driven by the specific interaction of eIF-4F p24 with the m7GTP cap structure; this is the first reported instance of only eIF-4B cross-linking to RNA.