Classes of aminoacyl-tRNA synthetases. Notice that class I and class II synthetases recognize different faces of the tRNA molecule. The CCA arm of tRNA adopts different conformations in complexes with the two classes of synthetase. Note that the CCA arm of the tRNA is turned toward the viewer (Figures 30.4 and 30.5).

[Drawn from 1EUY.pdb and 1QF6.pdb.]