Hydrolysis of the 5'-end of the nascent transcript by the capping enzyme After the capping complex is formed, the RNA triphosphatase activity of the capping enzyme hydrolyzes the 5'-end phosphate group of the nascent mRNA transcript to a diphosphate.<BR>The RNA triphosphatase (RTP) domain of mammalian capping enzyme is a member of a superfamily of phosphatases that include the protein tyrosine phosphatases, some lipid phosphatases, and several nucleic acid phosphatases. This family uses a conserved nucleophilic cysteine residue to attack the target phosphate. A transient phospho-cysteinyl enzyme intermediate is then hydrolyzed to regenerate the enzyme active site. It should be noted that while higher eukaryotic capping enzymes use PTP-like triphosphatase domains, the yeast triphosphatases are a completely different class of enzymes. The yeast RTPs are metal-dependent phosphatases. RNA 5'-triphosphatase (RTP) catalyzed first reaction can be represented as:pppN(pN)n + GTP -> ppN(pN)n + Pi; (n=20-25)<P> Authored: Buratowski, S, 2003-10-15 15:18:41 EC Number: 3.1.3.33 Pubmed9512541 Reactome Database ID Release 4377078 Reactome, http://www.reactome.org ReactomeREACT_1368 Capping complex (initial) Capping complex (hydrolyzed)