The 5' cap of eukaryotic messenger RNA is bound at all times by various cap-binding complexes (CBCs).

Nuclear cap-binding complex

In the nucleus, freshly transcribed mRNA molecules are bound on the 5' cap by the nuclear cap-binding complex of Cbc1/Cbc2 in yeast or CBP20/CBP80 in metazoans. These aid in the export of the mRNA and protect it from

decapping Decapping (decapsulation) or delidding of an integrated circuit is the process of removing the protective cover or integrated heat spreader (IHS) of an integrated circuit so that the contained die is revealed for visual inspection of the micro c ...

. They also serve as a marker for the so-called pioneer round of translation when the message is examined by nonsense mediated decay.

Cytoplasmic cap-binding complex

After the first round of translation ("pioneer round"), CBC20/80 is replaced by the

translation Translation is the communication of the Meaning (linguistic), meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The ...

initiation factor

eIF4E Eukaryotic translation initiation factor 4E, also known as eIF4E, is a protein that in humans is encoded by the ''EIF4E'' gene. Structure and function Most eukaryotic cellular mRNAs are blocked at their 5'-ends with the 7-methyl- guanosine ...

. The eIF4F complex (eIF4E,

eIF4G Eukaryotic translation initiation factor 4 G (eIF4G) is a protein involved in eukaryotic translation initiation and is a component of the eIF4F cap-binding complex. Orthologs of eIF4G have been studied in multiple species, including humans, yeast ...

and

eIF4A The eukaryotic initiation factor-4A (eIF4A) family consists of 3 closely related proteins EIF4A1, EIF4A2, and EIF4A3. These factors are required for the binding of mRNA to 40S ribosomal subunits. In addition these proteins are helicases tha ...

) then regulates translation in response to the state of the cell via its

phosphorylation In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, ...

state and again protects the message from decapping.

Decapping complex

When translationally repressed or marked for decay by various mechanisms the 5' cap is bound by the mRNA decapping enzyme DCP2. A host of proteins accompany it including

UPF1 Regulator of nonsense transcripts 1 is a protein that in humans is encoded by the ''UPF1'' gene. Function This gene encodes a protein that is part of a post-splicing multiprotein complex, the exon junction complex, involved in both mRNA nucle ...

, UPF2, UPF3A, Dcp1, Dhh1, XRN1, and others. The decapping enzyme removes the 5' cap leading to destruction of the message.

References

External links

* {{RNA-binding proteins RNA