Eukaryotic translation initiation factor 4E, also known as eIF4E, is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 which in humans is encoded by the eIF4E gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

.

Function

All eukaryotic

Eukaryote

A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

 cellular mRNA

Messenger RNA

Messenger RNA is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein...

s are modified at their 5-prime

Five prime untranslated region

A messenger ribonucleic acid molecule codes for a protein through translation. The mRNA also contains regions that are not translated: in eukaryotes these include the 5' untranslated region, 3' untranslated region, 5' cap and poly-A tail....

 ends with the 7-methyl-guanosine

Guanosine

Guanosine is a purine nucleoside comprising guanine attached to a ribose ring via a β-N9-glycosidic bond. Guanosine can be phosphorylated to become guanosine monophosphate , cyclic guanosine monophosphate , guanosine diphosphate , and guanosine triphosphate...

 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 ribosome

Ribosome

A ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....

s 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

Eif4a

The eukaryotic initiation factor-4A family consists of 3 closely related proteins EIF4A1, EIF4A2, and EIF4A3. These factors are required for the binding of mRNA to 40S ribosomal subunits...

, that possesses ATPase

ATPase

ATPases are a class of enzymes that catalyze the decomposition of adenosine triphosphate into adenosine diphosphate and a free phosphate ion. This dephosphorylation reaction releases energy, which the enzyme harnesses to drive other chemical reactions that would not otherwise occur...

 and RNA helicase

Helicase

Helicases are a class of enzymes vital to all living organisms. They are motor proteins that move directionally along a nucleic acid phosphodiester backbone, separating two annealed nucleic acid strands using energy derived from ATP hydrolysis.-Function:Many cellular processes Helicases are a...

 activities, and a 220-kD polypeptide, EIF4G

EIF4G

eIF4G is a protein involved in bringing mRNA to the ribosome for translation, generally based on mRNA's distinctive guanosine cap. Species versions of eIF4G have been studied in everything from humans, to yeast, to wheat...

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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, most notably heat shock proteins, don't require eIF4E in order to be translated. Both viruses and cellular proteins achieve this through an IRES structure in the RNA.

Interactions

EIF4E has been shown to interact

Protein-protein interaction

Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...

 with EIF4A1

EIF4A1

Eukaryotic initiation factor 4A-I is a protein that in humans is encoded by the EIF4A1 gene.-Interactions:EIF4A1 has been shown to interact with EIF4E and Eukaryotic translation initiation factor 4 gamma.-Further reading:...

, EIF4EBP3

EIF4EBP3

Eukaryotic translation initiation factor 4E-binding protein 3 is a protein that in humans is encoded by the EIF4EBP3 gene.-Further reading:...

, EIF4EBP1

EIF4EBP1

Eukaryotic translation initiation factor 4E-binding protein 1 is a protein that in humans is encoded by the EIF4EBP1 gene.-Interactions:EIF4EBP1 has been shown to interact with Mammalian target of rapamycin, EIF4E and KIAA1303.-Further reading:...

, EIF4EBP2

EIF4EBP2

Eukaryotic translation initiation factor 4E-binding protein 2 is a protein that in humans is encoded by the EIF4EBP2 gene.-Further reading:...

, Eukaryotic translation initiation factor 4 gamma

Eukaryotic translation initiation factor 4 gamma

Eukaryotic translation initiation factor 4 gamma 1 is a protein that in humans is encoded by the EIF4G1 gene.-Interactions:Eukaryotic translation initiation factor 4 gamma has been shown to interact with MKNK1, EIF4A1, EIF4E, MKNK2 and PABPC1....

, EIF4G2

EIF4G2

Eukaryotic translation initiation factor 4 gamma 2 is a protein that in humans is encoded by the EIF4G2 gene.-Interactions:EIF4G2 has been shown to interact with EIF4E and EIF3A.-Further reading:...

 and EIF4ENIF1

EIF4ENIF1

Eukaryotic translation initiation factor 4E transporter is a protein that in humans is encoded by the EIF4ENIF1 gene.-Interactions:EIF4ENIF1 has been shown to interact with EIF4E.-Further reading:...

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External links

• Cap-dependent translation initiation from Nature Reviews Microbiology. A good image and overview of the function of initiation factors

Further reading