Reactome: A Curated Pathway Database

mRNA Capping (R-HSA-72086)

Species Homo sapiens


The 5'-ends of all eukaryotic pre-mRNAs studied thus far are converted to cap structures. The cap is thought to influence splicing of the first intron, and is bound by 'cap-binding' proteins, CBP80 and CBP20, in the nucleus. The cap is important for translation initiation, and it also interacts with the poly(A)terminus, via proteins, resulting in circularization of the mRNA to facilitate multiple rounds of translation. The cap is also important for mRNA stability, protecting it from 5' to 3' nucleases, and is required for mRNA export to the cytoplasm.
The capping reaction usually occurs very rapidly on nascent transcripts; after the synthesis of only a few nucleotides by RNA polymerase II. The capping reaction involves the conversion of the 5'-end of the nascent transcript from a triphosphate to a diphosphate by a RNA 5'-triphosphatase, followed by the addition of a guanosine monophosphate by the mRNA guanylyltransferase, to form a 5'-5'-triphosphate linkage. This cap is then methylated by 2'-O-methyltransferases.

Locations in the PathwayBrowser
Additional Information
Compartment nucleoplasm
GO Biological Process 7-methylguanosine mRNA capping (0006370)
Literature References
pubMedId Title Journal Year
3326038 Messenger RNA capping enzymes from eukaryotic cells. Prog Nucleic Acid Res Mol Biol 1988
11909521 Integrating mRNA processing with transcription. Cell 2002
10395561 Coupling RNA polymerase II transcription with pre-mRNA processing. Curr Opin Cell Biol 1999
11017188 The ends of the affair: capping and polyadenylation. Nat Struct Biol 2000