Table 1. Translation initiation factors found in bacteria, archaea, and eukaryotes#.
| Bacteria | Archaea | Eukaryotes | # of subunits (name) | Function |
|---|---|---|---|---|
| IF11 | aIF1A1 | eIF1A1 | 1 | Binds SSU A site, blocking misloading of Met-tRNAi/fMet-tRNAf |
| IF21 | aIF5B1 | eIF5B1 | 1 | Binds GTP. GTP-bound form interacts with tRNAi acceptor stem and the SSU subunit interface to mediate the LSU joining. GTP hydrolysis promoted by LSU factor binding center. |
| IF32 | 1 | Anti-subunit re-association. Monitors correct tRNAf pairing with start codon. Bacteria-specific | ||
| aIF13 | eIF1*4 | 1 | Anti-subunit reassociation. Monitors correct tRNAi pairing with start codon | |
| aIF23 | eIF2*4 | 3 (α, β, γ) | Binds GTP and Met-tRNAi. GTP hydrolysis before start codon recognition. This is promoted by eIF5 in eukaryotes. | |
| eIF5*4 | 1 | Activates eIF2 GTPase (GAP) to control start codon recognition. Binds eIF1, eIF2 and eIF3 | ||
| eIF3*4 | Yeast, 6 (a-c, g, i, j) Mammals, 13 (a-m) |
Scaffold of assembly, to bind eIF1, eIF5, eIF4F and the 40S SSU | ||
| eIF2B | 5 (α−ε) | Guanine nucleotide exchange factor (GEF) for eIF2 | ||
| eIF4F | 3 (eIF4E, eIF4G, eIF4A) | Binds mRNA at its 5′ m7G cap structure and at its poly(A) tail. Contains eIF4A. | ||
| eIF4A | 1 | ATP-dependent mRNA helicase | ||
| eIF4B | 1 | Co-activator of eIF4A |