QARS (cytosolic glutaminyl tRNA synthetase) catalyzes the reaction of glutamine, tRNA(Gln), and ATP to form Gln-tRNA(Gln), AMP, and pyrophosphate. The enzyme, a class I tRNA synthetase, is found in the cell as a component of the mutienzyme aminoacyl-tRNA synthetase complex. The same gene encodes both the cytosolic and mitochondrial QARS enzymes (Lamour et al. 1994).