Fig. 6.

Cytosolic and organellar tRNA^Gln and Gln-tRNA^Gln forming enzymes. Cross-compartment sharing of tRNA and enzymes is observed in L. tarentolae (Lt) (2), T. brucei (Tb) (3), T. thermophila (Tt) (4), and S. cerevisiae (Sc) (5). At, A. thaliana; St, S. tuberosum; Hs, H. sapiens. In Lt, the mitochondrial GlnRS is distinct from the cytosolic one; by contrast, the same GlnRS is used in the cytosol and mitochondria of Tb and Sc. In Tt (1), GlnRS activities have similar specificities in the two compartments, and it is not excluded that the same enzyme is shared between the cytosol and the mitochondria. No mitochondrial GlnRS gene has been identified in Hs (2) (22).