Figure 1.

Chemical structures of presently known post-transcriptionally modified nucleosides from rRNA. A, archaea; B, bacteria; and E, eukarya. Symbols: m¹A, 1-methyladenosine; m²A, 2-methyladenosine; m⁶A, N⁶-methyladenosine; Am, 2′-O-methyladenosine; m⁶₂A, N⁶,N⁶-dimethyladenosine; Im, 2′-O-methylinosine; m³C, 3-methylcytidine; m⁴C, N⁴-methlycytidine; m⁵C, 5-methlycytidine; Cm, 2′-O-methylcytidine; ac⁴C, N⁴-acetylcytidine; m⁴Cm, N⁴,2′-O-dimethylcytidine; m⁴₂Cm, N⁴,N⁴,2′-O-trimethylcytidine; hm⁵C, 5-hydroxymethylcytidine; ac⁴Cm, N⁴-acetyl-2′-O-methylcytidine; m¹G, 1-methylguanosine; m²G, N²-methylguanosine; m⁷G, 7-methylguanosine; Gm, 2′-O-methylguanosine; m²₂G, N²,N²-dimethylguanosine; Ψ, pseudouridine; D, dihydrouridine; m³U, 3-methyluridine; m⁵U, 5-methyluridine; cm⁵U, 5-carboxymethyluridine; Um, 2′-O-methyluridine; m¹Ψ, 1-methylpseudouridine; m³Ψ, 3-methylpseudouridine; Ψm, 2′-O-methylpseudouridine; acp³U, 3-(3-amino-3-carboxypropyl)uridine; and m¹acp³Ψ, 1-methyl-3-(3-amino-3-carboxypropyl)pseudouridine.