Evolutionary convergence of G19–C56 tRNA base pair recognition. (A) PRORP1 PPR domain recognition of the G19–C56 base pair. (B) Bacterial RNP RNase P RNA recognition of the G19–C56 base pair (PDB ID: 3Q1Q). (C) 23S rRNA recognition of the G19–C56 base pair (PDB ID: 4V4I). (D) T-box riboswitch recognition of the G19–C56 base pair (PDB ID: 4LCK). PRORP1 PPR domain, RNase P RNA, 23S rRNA and T-box riboswitch in green are shown as cartoons with interacting residues displayed as stick models. Amino acid side chains and tRNA D-loop (light blue) and TψC-loop (orange) nucleotides are shown with atom colors: oxygen (red), nitrogen (blue), phosphorus (orange) and sulfur (yellow). Non-tRNA interacting nucleotides of bacterial RNase P, 23S rRNA and T-box riboswitch RNAs are shown as thin stick models.