Eukaryotic translation initiation factor 4E (eIF4E) binding site and the middle one-third of eIF4GI constitute the core domain for cap-dependent translation, and the C-terminal one-third functions as a modulatory region.
The mammalian eukaryotic initiation factor 4GI (eIF4GI) may be divided into three roughly equal regions; an amino-terminal one-third (amino acids [aa] 1 to 634), which contains the poly(A) binding protein (PABP) and eIF4E binding sites; a middle third (aa 635 to 1039), which binds eIF4A and eIF3; and a carboxy-terminal third (aa 1040 to 1560), which harbors a second eIF4A binding site and a docking sequence for the Ser/Thr kinase Mnk1. Previous reports demonstrated that the middle one-third of eIF4GI is sufficient for cap-independent translation. To delineate the eIF4GI core sequence required for cap-dependent translation, various truncated versions of eIF4GI were examined in an in vitro ribosome binding assay with beta-globin mRNA. A sequence of 540 aa encompassing aa 550 to 1090, which contains the eIF4E binding site and the middle region of eIF4GI, is the minimal sequence required for cap-dependent translation. In agreement with this, a point mutation in eIF4GI which abolished eIF4A binding in the middle region completely inhibited ribosomal binding. However, the eIF4GI C-terminal third region, which does not have a counterpart in yeast, modulates the activity of the core sequence. When the eIF4A binding site in the C-terminal region of eIF4GI was mutated, ribosome binding was decreased three- to fourfold. These data indicate that the interaction of eIF4A with the middle region of eIF4GI is necessary for translation, whereas the interaction of eIF4A with the C-terminal region plays a modulatory role.
Morino
S
S
Department of Biochemistry, McGill Cancer Center, McGill University, Montreal, Quebec H3G 1Y6, Canada.
Imataka
H
H
Svitkin
Y V
YV
Pestova
T V
TV
Sonenberg
N
N
D000595:Amino Acid Sequence; D001665:Binding Sites; D039601:Eukaryotic Initiation Factor-4A; D039561:Eukaryotic Initiation Factor-4E; D039603:Eukaryotic Initiation Factor-4G; D005914:Globins / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008954:Models, Biological; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010448:Peptide Initiation Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017354:Point Mutation / Q000235:genetics; D011233:Precipitin Tests; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000235:genetics*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012315:RNA Caps / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017384:Sequence Deletion / Q000235:genetics; D013698:Templates, Genetic
C113920:EIF4G1 protein, human; D039561:Eukaryotic Initiation Factor-4E; D039603:Eukaryotic Initiation Factor-4G; D047908:Intracellular Signaling Peptides and Proteins; D010446:Peptide Fragments; D010448:Peptide Initiation Factors; D012315:RNA Caps; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D005914:Globins; C491395:MKNK1 protein, human; D017346:Protein Serine-Threonine Kinases; D039601:Eukaryotic Initiation Factor-4A