Function
All eukaryotic cellular mRNAs are blocked at their 5-prime ends with the 7-methyl-guanosine cap structure, m7GpppX (where X is any nucleotide). This structure is involved in several cellular processes including enhanced translational efficiency, splicing, mRNA stability, and RNA nuclear export. EIF4E is a eukaryotic translation initiation factor involved in directing ribosomes to the cap structure of mRNAs. It is a 24-kD polypeptide that exists as both a free form and as part of a multiprotein complex termed EIF4F. The EIF4E polypeptide is the rate-limiting component of the eukaryotic translation apparatus and is involved in the mRNA-ribosome binding step of eukaryotic protein synthesis. The other subunits of EIF4F are a 50-kD polypeptide, termed EIF4A, that possesses ATPase and RNA helicase activities, and a 220-kD polypeptide, EIF4G.
eIF4E's function is to bind an mRNA cap and ultimately bring it to the ribosome. eIF4E is part of the eIF4F pre-initiation complex, which is made up of eIF4E, and eIF4G (eIF4F is sometimes considered to have additional protein components). Almost all cellular proteins require eIF4E in order to be translated into protein. eIF4E binds the first nucleotide on the 5' end of an mRNA molecule (known as the cap): a 7 methyl guanosine (m7G). It sandwiches m7G between 2 tryptophan residues, and other amino acids are involved in the binding.
Some viruses cut eIF4G in such a way that the eIF4E binding site is removed and the virus is able to translate its proteins without eIF4E. Also some cellular proteins, the most notable being heat shock proteins, do not require eIF4E in order to be translated. Both viruses and cellular proteins achieve this through an IRES structure in the RNA.
Read more about this topic: EIF4E
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