Extended Data Fig. 2: The canonical eukaryotic mRNA capping mechanism.
The 7MeGpppA2′-O-Me cap on eukaryotic RNA is formed co-transcriptionally by four enzymes: 1) an RNA triphosphatase (RTPase), which removes the γ-phosphate from the nascent 5′-triphosphorylated RNA (5′-pppRNA) to yield a 5′-diphosphorylated RNA (5′-ppRNA); 2) a guanylyltransferase (GTase), which transfers the GMP moiety from GTP to the 5′-ppRNA to form the core cap structure GpppN-RNA; 3) a (guanine-N7)-methyltransferase (N7-MTase), which methylates the cap guanine at the N7 position; and 4) a (nucleoside-2′-O)-methyltransferase (2′-O-MTase), which methylates the ribose-2′-OH position on the first nucleotide of the RNA. B denotes any base; GTP, Guanosine triphosphate; GDP, Guanosine diphosphate; PPi, pyrophosphate; SAM, S-Adenosyl methionine.
