The 5' cap

5' cap

The 5' cap is a specially altered nucleotide on the 5' end of precursor messenger RNA and some other primary RNA transcripts as found in eukaryotes. The process of 5' capping is vital to creating mature messenger RNA, which is then able to undergo translation...

 of eukaryotic messenger RNA

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...

 is bound at all times by various Cap-binding complexes.

Nuclear cap-binding complex

In the nucleus freshly transcribed mRNA molecules are bound on the 5' cap by the nuclear cap-binding complex

Nuclear cap-binding protein complex

Nuclear cap-binding protein complex is a RNA-binding protein which binds to the 5' cap of RNA polymerase II. The cap and nuclear cap-binding protein have many function in mRNA biogenesis including splicing, 3'-end formation by stabilizing the interaction of the 3'-end processing machinery, nuclear...

 of Cbc1/Cbc2 in yeast or CBC20/CBC80 in metazoans. These aid in the export of the mRNA and protect it from decapping

Messenger RNA decapping

The process of messenger RNA decapping consists of hydrolysis of the 5' cap structure on the RNA exposing a 5' monophosphate. This 5' monophosphate is a substrate for the exonuclease Xrn1 and the message is quickly destroyed...

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

Nonsense mediated decay

Nonsense-mediated decay is a cellular mechanism of mRNA surveillance that functions to detect nonsense mutations and prevent the expression of truncated or erroneous proteins. Following transcription, precursor mRNA undergoes an assemblage of ribonucleoprotein components followed by regulatory...

.

Cytoplasmic cap-binding complex

After the first round of translation the nuclear complex is replaced by the translation

Translation (genetics)

In molecular biology and genetics, translation is the third stage of protein biosynthesis . In translation, messenger RNA produced by transcription is decoded by the ribosome to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein...

 initiation factors eIF-4E and eIF-4G. These regulate translation in response to the state of the cell via their phosphorylation

Phosphorylation

Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....

 state and again protect 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

DCP2

mRNA-decapping enzyme 2 is a protein that in humans is encoded by the DCP2 gene.-Interactions:DCP2 has been shown to interact with DCP1A and UPF1.-Further reading:...

. A host of proteins accompany it including UPF1

UPF1

Regulator of nonsense transcripts 1 is a protein that in humans is encoded by the UPF1 gene.-Interactions:UPF1 has been shown to interact with UPF2, SMG1, DCP2, DCP1A, UPF3A and UPF3B.-Further reading:...

, UPF2

UPF2

Regulator of nonsense transcripts 2 is a protein that in humans is encoded by the UPF2 gene.-Interactions:UPF2 has been shown to interact with UPF1, UPF3A and UPF3B.-Further reading:...

, UPF3A

UPF3A

Regulator of nonsense transcripts 3A is a protein that in humans is encoded by the UPF3A gene.-Interactions:UPF3A has been shown to interact with RBM8A, UPF2 and UPF1.-Further reading:...

, Dcp1, Dhh1, XRN1

XRN1

XRN1 is an exoribonuclease enzyme. This enzyme is involves in 5’ to 3’ RNA degradation....

, and others. The decapping enzyme removes the 5' cap leading to destruction of the message.