Mammalian Translation Initiation Factor eIF1 Functions with eIF1A and eIF3 in the Formation of a Stable 40 S Preinitiation Complex

• Published in: The Journal of biological chemistry Vol. 278; no. 8; pp. 6580 - 6587
• Main Authors: Majumdar, Romit, Bandyopadhyay, Amitabha, Maitra, Umadas
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 21.02.2003
• Subjects: Animals; Eukaryotic Initiation Factor-1 - isolation & purification; Eukaryotic Initiation Factor-1 - metabolism; Eukaryotic Initiation Factor-3 - isolation & purification; Eukaryotic Initiation Factor-3 - metabolism; Guanosine Triphosphate - metabolism; Kinetics; Liver - metabolism; Peptide Chain Initiation, Translational - physiology; Peptide Initiation Factors - isolation & purification; Peptide Initiation Factors - metabolism; Protein Binding; Rabbits; Recombinant Proteins - isolation & purification; Recombinant Proteins - metabolism; Ribosomes - metabolism; RNA, Transfer, Met - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M210357200

We have examined the role of the mammalian initiation factor eIF1 in the formation of the 40 S preinitiation complex using in vitro binding of initiator Met-tRNA (as Met-tRNA i ·eIF2·GTP ternary complex) to 40 S ribosomal subunits in the absence of mRNA. We observed that, although both eIF1A and eIF3 are essential to generate a stable 40 S preinitiation complex, quantitative binding of the ternary complex to 40 S subunits also required eIF1. The 40 S preinitiation complex contained, in addition to eIF3, both eIF1 and eIF1A in a 1:1 stoichiometry with respect to the bound Met-tRNA i . These three initiation factors also bind to free 40 S subunits, and the resulting complex can act as an acceptor of the ternary complex to form the 40 S preinitiation complex (40 S·eIF3·eIF1·eIF1A·Met-tRNA i ·eIF2·GTP). The stable association of eIF1 with 40 S subunits required the presence of eIF3. In contrast, the binding of eIF1A to free 40 S ribosomes as well as to the 40 S preinitiation complex was stabilized by the presence of both eIF1 and eIF3. These studies suggest that it is possible for eIF1 and eIF1A to bind the 40 S preinitiation complex prior to mRNA binding.