Conserved amino acids near the carboxy terminus of bacterial tyrosyl-tRNA synthetase are involved in tRNA and Tyr-AMP binding.

Bacterial tyrosyl-tRNA synthetases occur in two large subfamilies, TyrRS and TyrRZ, that possess about 25% amino acid identity. Their amino-terminal region, the active site domain, is more conserved (>36% identity). The carboxy-terminal segment of these enzymes includes the tRNA binding domain and contains only few conserved residues. Replacement of three of these residues in Acidithiobacillus ferrooxidans TyrRZ revealed that S356 and K395 play roles in tRNA binding, while H306, a residue at the junction of the catalytic and tRNA binding domains, stabilizes the Tyr-AMP:TyrRZ complex. The replacement data suggest that conserved amino acids in A. ferrooxidans TyrRZ and Bacillus stearothermophilus TyrRS play equivalent roles in enzyme function.