FIGURE 1.

tRNA structure. Classical clover leaf fold presenting the standard base numbering. DHU and TѰC(R) loop domains corresponding to A and B boxes in eukaryotic tRNA genes are indicated. Principal interactions for the L-shape formation are shown in the upper left corner. Most frequent modified nucleosides in the tRNA anticodon are indicated. Derivatives of adenosine: t⁶A (N6-threonylcarbamoyladenosie), ms²t⁶A (2-methylthio-N6-threonylcarbamoyladenosine), ms²i⁶A (2-methylthio-N6-isopentenyladenosine), I (inosine), m¹I (1-methylinosine). Derivatives of cytidine: Cm (2′-O-methylcytidine), m⁵C (5-methylcytidine), m³C (3-methylcytidine), f⁵C (5 formylcytidine), k²C (lysidine), agm²C (agmatinylcytidine). Derivatives of guanosine: Gm (2′-O-methylguanosine), m¹G (1-methylguanosine), Q* and Q** (stand for queuosine in prokaryotes and eukaryotes, respectively), yW (wybutosine). Derivatives of uridine: cm⁵U (5-carboxymethyluridine), ncm⁵U (5-carbamoylmethyluridine), mcm⁵U (5-methoxycarbonylmethyluridine), mcm⁵s²U (5-methoxycarbonylmethyl-2-thiouridine), mcm⁵Um (5-methoxycarbonylmethyluridine), Ѱ (pseudouridine), s²U (2-thioruridine), tm⁵U (5-taurinomethyluridine) (see https://iimcb.genesilico.pl/modomics/) (Boccaletto et al., 2018). Pink indicates anticodon loop base modifications introduced by enzymes requiring cofactors and/or molecules involved in metabolic pathways. Blue boxes indicate modifications introduced by enzymes that do not require any cofactor.