The process of messenger RNA decapping consists of hydrolysis of 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...

 structure on the RNA exposing a 5' monophosphate. This 5' monophosphate is a substrate for the exonuclease

Exonuclease

Exonucleases are enzymes that work by cleaving nucleotides one at a time from the end of a polynucleotide chain. A hydrolyzing reaction that breaks phosphodiester bonds at either the 3’ or the 5’ end occurs. Its close relative is the endonuclease, which cleaves phosphodiester bonds in the middle ...

 Xrn1 and the message is quickly destroyed. There are many situations which may lead to the removal of the cap, some of which are discussed below.

Translation and Decay

Inside cells there is a balance between the processes of 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...

 and mRNA decay. Messages which are being actively translated are bound by polysome

Polysome

Polyribosomes also known as ergosomes are a cluster of ribosomes, bound to a mRNA molecule, first discovered and characterized by Jonathan Warner, Paul Knopf, and Alex Rich in 1963. Many ribosomes read one mRNA simultaneously, progressing along the mRNA to synthesize the same protein...

s and the initiation factors eIF-4E and eIF-4G. This blocks access to the cap by the 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:...

 and protects the message. In nutrient-starvation conditions or viral infection, translation may be compromised and decapping is stimulated. This balance is reflected in the size and abundance of the cytoplasmic structures known as P-bodies

P-bodies

Processing bodies were first described in the scientific literature by Bashkirov et. al. in 1997, in which they describe "small granules… discrete, prominent foci" as the cytoplasmic location of the mouse exoribonuclease mXrn1p. It wasn’t until 2002 that a glimpse into the nature and importance of...

 

Specific decay pathways

A number of specific decay pathways exist that recognize aberrant messages and promote their decapping. 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...

 recognizes premature stop codons and promotes decapping as well as decay by the exosome

Exosome complex

The exosome complex is a multi-protein complex capable of degrading various types of RNA molecules...

. Certain classes of miRNA have also been shown to stimulate decapping.