The process of 5' capping is catalyzed by a series of enzymatic reactions. First, an enzyme named RNA triphosphatase removes one phosphate group from the 5' end of the nascent RNA. Next, guanylyl transferase adds a GMP (guanosine monophosphate) to the 5' diphosphate end, forming a 5'-5' triphosphate linkage. Finally, a methyl group is added to the guanine nucleotide by guanine N7-methyltransferase, resulting in the formation of the 7-methylguanosine cap.
