 Three enzymes, RNA triphosphatase, guanylyltransferase (or CE), and methyltransferase are involved in the addition of the methylated 5' cap to the mRNA.Capping is a three-step process that utilizes the enzymes RNA triphosphatase, guanylyltransferase, and methyltransferase.Through a series of three steps, the cap is added to the first nucleotide's 5' hydroxyl group of the growing mRNA strand while transcription is still occurring.