title: The p46 subunit of eukaryotic initiation factor (eIF)-4F exchanges with eIF-4A.
abstract: The p46 subunit of eukaryotic initiation factor (eIF)-4F purified from rabbit reticulocyte lysate has previously been found to be composed of eIF-4AI and eIF-4AII in a 4:1 ratio, respectively, whereas the free form of rabbit eIF-4A is composed solely of eIF-4AI. Using sucrose gradient centrifugation and an m7GTP-Sepharose 4B assay, it was shown that eIF-4A exchanges with the p46 subunit of eIF-4F. Incubation of [14C]eIF-4A and eIF-4F resulted in the incorporation of [14C] eIF-4A into the eIF-4F complex. Conversely, the [14C] p46 subunit of [14C]eIF-4F was shown to dissociate from the [14C]eIF-4F complex in the presence of eIF-4A, presumably due to the incorporation of unlabeled eIF-4A. Similar experiments were conducted in which 14C-labeled initiation factors were incubated with rabbit reticulocyte lysate. When [14C]eIF-4A was incubated with lysate, [14C]eIF-4A became incorporated into the eIF-4F complex present in the lysate. Additionally, when [14C]eIF-4F was incubated with lysate, the [14C]p46 subunit of [14C]eIF-4F dissociated from the [14C]eIF-4F complex, most likely due to the exchange of unlabeled eIF-4A (present in the lysate) with the [14C]p46 subunit. The exchange of mouse eIF-4AI and eIF-4AII expressed in Escherichia coli was also investigated in the presence of eIF-4F and rabbit reticulocyte lysate. Both the sucrose gradient experiments and m7GTP-Sepharose 4B assays demonstrated that the [14C]p46 subunit of [14C]eIF-4F was displaced in the presence of eIF-4AI or eIF-4AII and that mouse [14C]eIF-4AI or [14C]eIF-4AII became incorporated into the eIF-4F complex in the same manner as rabbit reticulocyte eIF-4A.
authors.affiliation: Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106.
authors.forename: J
authors.initials: J
authors.lastname: Yoder-Hill
authors.forename: A
authors.initials: A
authors.lastname: Pause
authors.forename: N
authors.initials: N
authors.lastname: Sonenberg
authors.forename: W C
authors.initials: WC
authors.lastname: Merrick
mesh_terms: D000818:Animals; D003001:Cloning, Molecular; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli; D039601:Eukaryotic Initiation Factor-4A; D039562:Eukaryotic Initiation Factor-4F; D051379:Mice; D010446:Peptide Fragments / Q000378:metabolism; D010448:Peptide Initiation Factors / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes
chemical_list: D039562:Eukaryotic Initiation Factor-4F; D010446:Peptide Fragments; D010448:Peptide Initiation Factors; D039601:Eukaryotic Initiation Factor-4A