Messenger RNA decapping

In eukaryotes, this 5' monophosphate is a substrate for the 5' exonuclease Xrn1[1] and the mRNA is quickly destroyed.

[2] In prokaryotes, the initial mRNA transcript naturally possesses a 5'-triphosphate group after bacterial transcription; the enzyme RppH removes a pyrophosphate molecule from the 5' end, converting the 5'-triphosphate to a 5'-monophosphate, triggering mRNA degradation by ribonucleases.

This blocks access to the cap by the decapping enzyme DCP2 and protects the mRNA molecule.

In nutrient-starvation conditions or viral infection, translation may be compromised and decapping is stimulated.

[5][6] A number of specific decay pathways exist that recognize aberrant messages and promote their decapping.