eIF1A

eIF1A consists of 143-151 amino acids and is highly charged, consisting of acidic and basic regions at its N and C termini (Dever et al., 1994). It is an RNA-binding protein (Wei et al., 1995) and NMR studies have validated this through identifying the architecture of a RNA-binding surface of which presently no ligand is known to bind (Battiste et al., 2000). The eIF1A factor is highly interchangeable between species, such as wheat and rabbit in vitro and human and yeast in vivo (Wei et al., 1995). However, eIF1A is unique from most other initiation factors, by having a high degree of sequence homology to prokaryotic initiation factor IF1 (Kyripides and Woese, 1998). Structures of Escherichia coli IF1 and human eIF1A are very similar over a conserved region consisting of a beta barrel fold, depicting that similar functions may be implicated in both prokaryotic IF1 and eukaryotic eIF1A.

Recently, Pestova and colleagues purified eIFs and 40S ribosomal subunits and viewed the formation of initiation complexes, with the presence and absence of factors by sucrose density-gradient centrifugation. They discovered that eIFs 2, 3, 4A, 4B and 4F are sufficient for attachment of a ribosome to capped mRNA but not to begin searching for the initiation site (Pestova et al., 1998). Formation of a downstream complex occured in the presence of eIF1, with a greater majority of complexes being present with the addition of eIF1A. It is thought that eIF1A increases the ability of the 43S complex to scan downstream mRNA codons, by enhancing its stability on mRNA, due to eIF1A being a strong RNA-binding protein (Wei et al., 1995). These factors may be involved in the correct interactions of the 43S complex with mRNA that enable it to become processive, by forming a psrt of the channel through which mRNA moves during ribosomal scanning or by contributing to the ribosomal translocation process (Peskova et al., 1998).