of an RNA molecule, which terminates at a triphosphate group. This features a final nucleotide followed by three phosphate groups attached to the 5´ carbon. The capping process is initiated before the completion of transcription, as the nascent pre-mRNA is being synthesized.

# One of the terminal phosphate groups is removed by RNA triphosphatase, leaving a bisphosphate group (i.e. 5´(ppN)[pN]_n);
# GTP is added to the terminal