Phyletic Distribution and Conserved Domains in Components of the Eukaryotic Translation Initiation System
| Protein/GI number[i] | Phyletic distribution[ii] | Domain organization[iii] | Structural class of conserved domain | Comments |
| eIF1 (SUI1) 4240113 | EAB [Bacteria = Ec, Hi, Ssp] | Sui1 domain | α + β | Probably horizontally transferred into bacteria |
| eIF1A (eIF4C) 626955 | EAB | OB-fold domain | β | Bacterial IF1 ortholog |
| IF2 (eIF5B) 1723187 | EAB | Multidomain GTPase | α + β | Ortholog of bacterial IF2, appears to be necessary for joining of the 2 ribosomal subunits in both eukaryotes and bacteria |
| eIF2α 124203 | EA | S1 RNA-binding domain | β | |
| eIF2β 4503505 | EA | Zinc ribbon | β | A similar Zn-ribbon found in eIF5 |
| eIF2γ 3790165 | EA(B) | GTPase (Zn-ribbon insertion) | α + β | The most similar bacterial homologs are elongation factors SelB/EF-TU |
| eIF2Bα 2494303 eIF2Bβ 2661031 eIF2Bδ 417036 | EAB [Bacteria = Ssp, Bs, Tma, Rhoru] | α-helical DEF domain for the eIF2 GTPase | α | Probably horizontally transferred into bacteria |
| eIF2Bγ 2506383 | E(AB) | Nucleotidyltransferase + I-patch repeats | α + β | Several bacteria encode homologous proteins that are unlikely to function in translation |
| eIF2Bɛ 2408098 | E(AB) | Nucleotidyltransferase + I-patch repeats + W2 | α + β and α | Several bacteria encode homologous proteins that are unlikely to function in translation |
| eIF2C 3253159 | EAB [Bacteria = Aae] | Argonaute homolog | α + β | Apparent horizontal transfer from archaea to Aquifex. Expansion of this family in C. elegans |
| eIF3-p39 (TIF34p) 6323795 | E | WD40-β-propeller | β | Probable mRNA-binding subunit |
| eIF3-p40 2351380 | E(AB) | JAB/PAD domain | α + β | Related to/part of the signalosome complex |
| eIF3-p44 (TIF35p) 6320637 | E | C-terminal RRM | α + β | |
| eIF3-p47 2055431 | E(AB) | JAB/PAD domain | α + β | Related to/part of the signalosome complex. Missing in S. cerevisiae |
| eIF3-p48 2351382 | E | PINT domain | α | Related to/part of the signalosome complex. Missing in S. cerevisiae |
| eIF3-p66 2351378 | E | ? | ? | Related to/part of the signalosome complex. Missing in S. cerevisiae |
| eIF3-p110 (NIP1) 1718197 | E | PINT domain | α | Related to/part of the signalosome complex |
| eIF3-p116 (PRT1p) 3123230 | E | RRM + β-propeller | α + β and β | Probable mRNA-binding subunit |
| eIF3-p150 | E | ? | α | |
| eIF3-p162 (TIF32p) 2580607 | E | ? | α | |
| eIF4A 6322912 | E(AB) | Superfamily II helicase | α + β | |
| eIF4B 464817 | E | Two RRM domains | α + β | |
| eIF4E 1352435 | E | Unique α/β fold | α + β | 25 kD subunit of eIF4F |
| eIF4G 3941724 | E | NIC domain NIC + MI NIC + MI + W2 | α | Other domains added to the NIC domain in certain eukaryotic lineages. 150kD subunit of eIF4F |
| eIF4H 2914759 | E | RRM | α + β | Closely related to eIF2B, appears to be vertebrate-specfic |
| eIF5 1708419 | E | Zn ribbon + W2 | β and α | The Zn-ribbon is closely related to the ribbon in eIF2 β subunit. A related ribbon is seen in Archaea as a stand-alone protein |
| eIF5A (eIF4D) 124229 | EAB | OB fold protein | β | The bacterial ortholog is EF-P. Eukaryotic eIF5A contains a lysine to hypusine modification that is necessary for function. |
| eIF6 6325273 | EA | Duplication of a unique domain | ? |
[i] For each factor, a Gene Identification (GI) number of a representative eukaryotic sequence is given to ensure unambiguous identification in databases
[ii] E—eukaryotes, A—archaea, B—bacteria. In cases when bacteria and/or archaea encoded homologs of the respective eukaryotic factor that do not seem to be true orthologs, B and/or A is indicated in parentheses. When the distribution of the orthologs of the respective eukaryotic factor in bacteria is sporadic, the species encoding it are indicated in square brackets. Species abbreviations: Aae—Aquifex aeolicus, BS—Bacillus subtilis,Ec—Escherichia coli, Hi—Haemophilus influenzae,Rhoru—Rhospirillum rubrum, Ssp—Synechocystis sp, Tma—Thermotoga maritima.
[iii] A question mark indicates absence of distinct, recognizable domains.