Aminoacyl-tRNA synthetases (aaRSs) catalyze the ligation of amino acids to their cognate tRNAs, allowing them to decode the triplet code during translation (EC:6.1.1.-). aaRSs may be classified based on their protein structure: class I aaRSs contain a characteristic Rossman fold catalytic domain and usually function as monomeric or dimeric proteins, while class II aaRSs contain 3 conserved motifs and are usually dimeric or tetrameric. Alternatively, aaRSs may be classified according to their subcellular sites of action - cytoplasmic, mitochondrial, or both cytoplasmic and mitochondrial ('dual-localized') - which is the system adopted here. (Adapted from FBrf0230668.)