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