Figure 2.

Variability of tRNA modifications. The upper part of the image illustrates the systematic abbreviation of RNA modifications with N²,N²,2′-O-trimethylguanosine (m²₂Gm) as an example and also shows the atom numbering in the purine and pyrimidine rings as well as in the ribose. An abbreviation in front of the base letter describes a base modification, whereas letters after the base stand for ribose alterations. Superscripted numbers specify the position at the base and subscripted numbers indicate the frequency of identical modification at the same position. Abbreviations are as follows: ac—acetyl, acp—aminocarboxypropyl, chm—carboxyhydroxymethyl, cmo—oxyacetic acid, cmnm—carboxymethylaminomethyl, f—formyl, g—glycinyl, gal—galactosyl, hn—hydroxynorvalylcarbamoyl, ho—hydroxy, i—isopentenyl, inm—isopentenylaminomethyl, io—cis-hydroxyisopentenyl, m—methyl, man—mannosyl, mchm—carboxyhydroxymethyl methyl ester, mcm—methoxycarbonylmethyl, mcmo—oxyacetic acid methyl ester, mnm—methylaminomethyl, mo—methoxy, ncm—carbamoylmethyl, nm—aminomethyl, r(p) —5-O-phosphono-b-d-ribofuranosyl, s—thio, se—seleno, t—threonylcarbamoyl, tm—taurinomethyl. The Venn diagram summarizes data collected from the RNA modification database and contains the 93 post-transcriptional modifications that are found in tRNAs [5]. Some examples mentioned throughout the text are shown with their chemical structure.