Eukaryotic translation initiation factor 1 is a protein that in humans is encoded by the EIF1gene.
Mammalian 17-kDa eukaryotic initiation factor, eIF1A (formerly designated eIF-4C), is essential for transfer of the initiator Met-tRNAf (as Met-tRNAf·eIF2·GTP ternary complex) to 40 S ribosomal subunits in the absence of mRNA to form the 40 S preinitiation complex (40 S·Met-tRNAf·eIF2·GTP). Furthermore, eIF1A acts catalytically in this reaction to mediate highly efficient transfer of the Met-tRNAf·eIF2·GTP ternary complex to 40 S ribosomal subunits. The 40 S complex formed is free of eIF1A which indicates that its role in 40 S preinitiation complex formation is not to stabilize the binding of Met-tRNAf to 40 S ribosomes. Additionally, the eIF1A-mediated 40 S initiation complex formed in the presence of AUG codon efficiently joins 60 S ribosomal subunits in an eIF5-dependent reaction to form a functional 80 S initiation complex. Though found in some reports, eIF1A probably plays no role either in the subunit joining reaction or in the generation of ribosomal subunits from 80 S ribosomes. The major function of eIF1A is to mediate the transfer of Met-tRNAf to 40 S ribosomal subunits to form the 40 S preinitiation complex.
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