label: a 5'-end triphospho-(purine-ribonucleoside) in mRNA + GDP + H(+) => a 5'-end (5'-triphosphoguanosine)-(purine-ribonucleoside) in mRNA + diphosphate
label_lc: a 5'-end triphospho-(purine-ribonucleoside) in mrna + gdp + h(+) => a 5'-end (5'-triphosphoguanosine)-(purine-ribonucleoside) in mrna + diphosphate