N(7)-methyl-GMP + a 5'-end diphospho-(purine-ribonucleoside) in mRNA + 2 H(+) => a 5'-end (N(7)-methyl 5'-triphosphoguanosine)-(purine-ribonucleoside) in mRNA + H2O
n(7)-methyl-gmp + a 5'-end diphospho-(purine-ribonucleoside) in mrna + 2 h(+) => a 5'-end (n(7)-methyl 5'-triphosphoguanosine)-(purine-ribonucleoside) in mrna + h2o