label: N(2),N(2),N(7)-trimethyl-GDP + a 5'-end phospho-ribonucleoside in mRNA + 2 H(+) => a 5'-end (N(2),N(2),N(7)-trimethyl 5'-triphosphoguanosine)-ribonucleoside in mRNA + H2O
label_lc: n(2),n(2),n(7)-trimethyl-gdp + a 5'-end phospho-ribonucleoside in mrna + 2 h(+) => a 5'-end (n(2),n(2),n(7)-trimethyl 5'-triphosphoguanosine)-ribonucleoside in mrna + h2o