ID 6.5.1.5 DE RNA 3'-terminal-phosphate cyclase (GTP). AN RNA-3'-phosphate cyclase (GTP). CA a 3'-end 3'-phospho-ribonucleotide-RNA + GTP = a 3'-end CA 2',3'-cyclophospho-ribonucleotide-RNA + diphosphate + GMP. CC -!- The enzyme, which is specific for GTP, was characterized from the CC archaeon Pyrococcus furiosus. CC -!- The enzyme converts the 3'-terminal phosphate of various RNA CC substrates into the 2',3'-cyclic phosphodiester in a GTP-dependent CC reaction. CC -!- Catalysis occurs by a three-step mechanism, starting with the CC activation of the enzyme by GTP, forming a phosphoramide bond between CC guanylate and a histidine residue. CC -!- The guanylate group is then transferred to the 3'-phosphate terminus CC of the substrate, forming the capped structure [RNA]- CC 3'-(5'-diphosphoguanosine). CC -!- Finally, the enzyme catalyzes an attack of the vicinal O-2' on the CC 3'-phosphorus, which results in formation of cyclic phosphate and CC release of the guanylate. cf. EC 6.5.1.4. DR Q8U0N7, RTCA_PYRFU ; //