N6-Methyladenosine - 13 C 4 (6-Methyladenosine- 13 C 4 ; N-Methyladenosine- 13 C 4 ) is 13 C-labeled N6-Methyladenosine. N6-Methyladenosine is the most prevalent internal (non-cap) modification present in the messenger RNA ( mRNA ) of all higher eukaryotes. N6-Methyladenosine can modifies viral RNAs and has antiviral activities.