page_title: EIF2
section_title: Function
hierarchical_section_title: EIF2 / Function
caption_attribution_description: English: The scheme of cap-dependent eukaryotic translation initiation mechanism 中文（简体）‎: Cap依赖的真核翻译起始机制简图
context_page_description: Eukaryotic Initiation Factor 2 is a eukaryotic initiation factor. It is required for most forms of eukaryotic translation initiation. eIF2 mediates the binding of tRNAᵢᴹᵉᵗ to the ribosome in a GTP-dependent manner. eIF2 is a heterotrimer consisting of an alpha, a beta, and a gamma subunit.
  Once the initiation phase has completed, eIF2 is released from the ribosome bound to GDP as an inactive binary complex. To participate in another round of translation initiation, this GDP must be exchanged for GTP.
context_section_description: eIF2 is an essential factor for protein synthesis that forms a ternary complex (TC) with GTP and the initiator Met-tRNAᵢᴹᵉᵗ. After its formation, the TC binds the 40S ribosomal subunit to form the 43S preinitiation complex (43S PIC). 43S PIC assembly is believed to be stimulated by the initiation factors eIF1, eIF1A, and the eIF3 complex according to in vitro experiments. The 43S PIC then binds mRNA that has previously been unwound by the eIF4F complex. The 43S PIC and the eIF4F proteins form a new 48S complex on the mRNA, which starts searching along the mRNA for the start codon (AUG). Upon base pairing of the AUG-codon with the Met-tRNA, eIF5 (which is a GTPase-activating protein , or GAP) is recruited to the complex and induces eIF2 to hydrolyse its GTP. This causes eIF2-GDP to be released from this 48S complex and translation begins after recruitment of the 60S ribosomal sub-unit and formation of the 80S initiation complex. Finally, with the help of the guanine nucleotide exchange factor (GEF) eIF2B, the GDP in eIF2 is exchanged for a GTP and the ternary complex reforms for a new round of translation initiation.
caption: The process of initiation of translation in eukaryotes with eIF2 in light-green. Other factors are shown, too.
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