label: a 5'-end diphospho-ribonucleoside in mRNA + GTP + H(+) <=> a 5'-end (5'-triphosphoguanosine)-ribonucleoside in mRNA + diphosphate
label_lc: a 5'-end diphospho-ribonucleoside in mrna + gtp + h(+) <=> a 5'-end (5'-triphosphoguanosine)-ribonucleoside in mrna + diphosphate