Fig. 2.

Nucleotide-binding pocket of a class I CCA-adding enzyme with templating region. A highly conserved arginine residue of the enzyme (green) as well as phosphate groups of the tRNA backbone (grey) form specific hydrogen bonds with the bound nucleotides (red). The collaboration of both protein and tRNA is responsible for an efficient and accurate templating during CCA-addition. The shown structures are parts of the pdb entries of the A. fulgidus CCA-adding enzyme [33]