Fig. 3. Ribbon diagrams of single subunits of representatives of each of the five class IIa tRNA synthetases. All have the class II catalytic domain aligned in the same orientation with motifs 1, 2 and 3 shown in green, cyan and red, respectively. All except SerRS (top right) have the class IIa anticodon-binding domain (purple). System-specific domains are shown in yellow.