 First, RNA 5' triphosphatase hydrolyzes the 5' triphosphate group to make diphospate-RNA.Then, the addition of GMP by guanylyltransferase produces the guanosine cap.Last, RNA methyltransferase transfers a methyl group to the guanosine cap to yield 7-methylguanosine cap that is attached to the 5' end of the transcript.