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