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. Author manuscript; available in PMC: 2015 Jun 9.
Published in final edited form as: Nat Rev Mol Cell Biol. 2010 Feb;11(2):113–127. doi: 10.1038/nrm2838

Table 1.

Eukaryotic initiation factors

Name Subunits Mol. wt. (kDa) Function
Core Initiation Factors
eIF2 3 (36.1, 38.4, 51.1) Forms an eIF2/GTP/Met-tRNAi ternary complex that binds to the 40S subunit, thus mediating ribosomal recruitment of Met-tRNAi
eIF3 13 (800 total) Binds 40S subunits, eIFs 1, 4G, 5; stimulates binding of eIF2/GTP/Met-tRNAi to 40S subunits; promotes attachment of 43S complexes to mRNA and subsequent scanning; possesses ribosome dissociation and anti-association activities preventing joining of 40S and 60S subunits
eIF1 1 (12.7) Ensures the fidelity of initiation codon selection; promotes ribosomal scanning; stimulates binding of eIF2/GTP/Met-tRNAi to 40S subunits; prevents premature eIF5-induced hydrolysis of eIF2-bound GTP and Pi release
eIF1A 1 (16.5) Stimulates binding of eIF2/GTP/Met-tRNAi to 40S subunits; cooperates with eIF1 in promoting ribosomal scanning and initiation codon selection
eIF4E 1 (24.5) Binds to the m7GpppG 5’-terminal ‘cap’ structure of mRNA
eIF4A* 1 (46.1) DEAD-box ATPase and ATP-dependent RNA helicase
eIF4G** 1 (175.5) Binds eIF4E, eIF4A, eIF3, PABP, SLIP1 and mRNA (Fig. 3A); enhances eIF4A’s helicase activity
eIF4F 3 (246.1 total) Cap-binding complex, comprising eIF4E, eIF4A and eIF4G; unwinds 5’-proximal region of mRNA and mediates attachment to it of 43S complexes; assist ribosomal complexes during scanning
eIF4B 1 (69.3) RNA-binding protein; enhances eIF4A’s helicase activity
eIF4H 1 (27.4) RNA-binding protein; enhances eIF4A’s helicase activity; homologous to a fragment of eIF4B
eIF5 1 (49.2) GTPase-activating protein specific for eIF2•GTP that induces hydrolysis of eIF2-bound GTP upon recognition of the initiation codon
eIF5B 1 (138.9) Ribosome-dependent GTPase; mediates ribosomal subunit joining
eIF2B 5 (33.7, 39.0, 50.2, 59.7, 80.3) Guanosine nucleoside exchange factor that promotes GDP/GTP exchange on eIF2
Auxiliary factors
DHX29 1 (155.3) A DExH-box-containing protein; binds 40S subunit; promotes ribosomal scanning on mRNAs with long, highly-structured 5’UTRs
Ded1p 1 (65.6) DEAD-box NTPase/RNA helicase; potentially promotes scanning in S. cerevisiae
eIF6 1 (26.6) Binds 60S subunits; anti-association factor that prevents joining of 40S subunits to 60S subunits
p97 1 (102.4) Closely related to the carboxy-terminal two-thirds of eIF4GI; binds eIF4A and eIF3; promotes initiation in a potentially mRNA-specific manner
PABP 1 (70.7) Binds to the mRNA 3’-poly(A) tail, eIF4G and eRF3; enhances binding of eIF4F to the cap; may facilitate recruitment of recycled post-termination 40S subunits back to the 5’-end of mRNA.
*

Two paralogues (eIF4AI and eIF4AII), encoded by different genes, are functionally indistinguishable, but “eIF4AIII” has no activity as an eIF.

**

Two paralogues (eIF4GI and eIF4GII), encoded by different genes, are functionally similar but show some selectivity towards different mRNAs. eIF4GI is generally the more abundant.