RNGTT and viral infectious disease: The 5′ end of the dengue, yellow fever, and West Nile virus genomic RNA is conserved as an “5′-AG(U/A)” sequence, and we observed that a 5′ ppAG terminated RNA not related to a flavivirus 5′ UTR can be capped by the capping enzyme [7], indicating that only the very 5′ base sequences of the RNA are necessary for the GTase reaction and that RNA structures important for MTase activity are not necessary for the RNA guanyltransfer step [16], [17].