(Figure 10.23a). This Class I synthetase binds on one side of the tRNA and contacts the sugar–phosphate
backbone and the minor grooveside of the acceptor stem. The acceptor stem is recognized by ‘indirect read-
out’ determined by the conformation of the CCA end. By contrast, the structure of the complex between
the Class II yeast aspartyl-tRNA synthetase and its cognate tRNA shows that this enzyme binds tRNA
from the major grooveside (Figure 10.23b).
It may seem surprising that the determinants of recognition do not in all cases involve directly the anti-
codon triplet, but instead are often distributed throughout the tRNA. For example, the structure of seryl-
tRNA synthetase complexed with tRNA (Figure 10.23c) shows a distinctive mode of recognition where an
420 Chapter 10
Figure 10.23 Representative amino acyl tRNA synthetases showing different modes of RNA–protein recognition.
(a) Glutamyl-tRNA synthetase (PDB: 1N77). (b) Aspartyl-tRNA syntetase (PDB: 1JGO). (c) Seryl-
tRNA synthetase (PDB: 1SER)