A capping enzyme
is a guanylyl transferase enzyme
the attachment of the 5' cap
to messenger RNA
molecules that are in the process of being synthesized in the cell nucleus
during the first stages of gene expression
. The addition of the cap occurs co-transcriptionally
, after the growing RNA
molecule contains about 30 nucleotides
. The enzyme can only catalyze its reaction when bound to the phosphorylated
carboxyl-terminal domain of RNA polymerase II
; therefore it is specific to RNAs synthesized by this polymerase rather than those synthesized by RNA polymerase I
or RNA polymerase III
- Lodish H, Berk A, Matsudaira P, Kaiser CA, Krieger M, Scott MP, Zipursky SL, Darnell J. (2004). Molecular Cell Biology. WH Freeman: New York, NY. 5th ed.
- Hakansson, K., Wigley, D.B. (1998). Structure of a complex between a cap analogue and mRNA guanylyl transferase demonstrates the structural chemistry of RNA capping. Proc Natl Acad Sci USA 95:1505-1510.