The pseudo-dimeric tyrosyl-tRNA synthetase of T. brucei aminoacylates cytosolic and mitochondrial tRNA Tyr and requires both monomeric units for activity.

Aminoacyl-tRNA synthetases are essential for protein synthesis. The single-copy tyrosyl-tRNA synthetase (Tb-TyrRS) of T. brucei has an unusual structure and forms a pseudo-dimer. It is therefore twice the size than tyrosyl-tRNA synthetases of most other organisms. Here we show by inducible RNAi that Tb-TyrRS is essential for normal growth of procyclic T. brucei. Furthermore we demonstrate that Tb-TyrRS aminoacylates cytosolic as well as mitochondrial tRNATyr indicating that it is dually localized. Finally we show that individual deletion of the 36 N- or C-terminal amino acids abolishes the function of Tb-TyrRS. This indicates that both monomeric units of the enzyme, the C-terminal one of which is predicted to lack enzymatic activity, are essential for Tb-TyrRS function. In summary our results together with previous studies support the notion that Tb-TyrRS might be a suitable drug target.