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