EC Explorer

6.5.1.5

RNA 3′-terminal-phosphate cyclase (GTP)

GTP + [RNA]-3′-(3′-phospho-ribonucleoside) = GMP + diphosphate + [RNA]-3′-(2′,3′-cyclophospho)-ribonucleoside (overall reaction);;(1a) GTP + [RNA 3′-phosphate cyclase]-L-histidine = 5′-guanosyl [RNA 3′-phosphate cyclase]-N^τ-phosphono-L-histidine + diphosphate;;(1b) 5′-guanosyl [RNA 3′-phosphate cyclase]-N^τ-phosphono-L-histidine + [RNA]-3′-(3′-phospho-ribonucleoside) = [RNA 3′-phosphate cyclase]-L-histidine + [RNA]-3′-ribonucleoside-3′-(5′-diphosphoguanosine);;(1c) [RNA]-3′-ribonucleoside-3′-(5′-diphosphoguanosine) = [RNA]-3′-(2′,3′-cyclophospho)-ribonucleoside + GMP

Pf-Rtc, RNA-3′-phosphate cyclase (GTP)

RNA-3′-phosphate:RNA ligase (cyclizing, GMP-forming)

The enzyme, which is specific for GTP, was characterized from the archaeon Pyrococcus furiosus. The enzyme converts the 3′-terminal phosphate of various RNA substrates into the 2′,3′-cyclic phosphodiester in a GTP-dependent reaction. Catalysis occurs by a three-step mechanism, starting with the activation of the enzyme by GTP, forming a phosphoramide bond between guanylate and a histidine residue. The guanylate group is then transferred to the 3′-phosphate terminus of the substrate, forming the capped structure [RNA]-3′-(5′-diphosphoguanosine). Finally, the enzyme catalyses an attack of the vicinal O-2′ on the 3′-phosphorus, which results in formation of cyclic phosphate and release of the guanylate. cf. EC 6.5.1.4, RNA-3′-phosphate cyclase (ATP).

created 2013, modified 2016