Model of the enzymatic pathway for the Apg12p-Apg5p conjugation system. Apg12p is activated by Apg7p with ATP hydrolysis; the carboxy group of the C‐terminal glycine of Apg12 is conjugated to the thiol group of the cysteine‐507 residue of Apg7p via a high‐energy thioester bond (∼). Subsequent transfer of Apg12p to the thiol group of the cysteine‐133 residue of Apg10p results in the formation of the Apg12p-Apg10p thioester. Finally, the C‐terminus of Apg12p is covalently attached to the lysine‐149 residue of Apg5p via an isopeptide bond, which may require hypothetical Apg5p‐recognizing protein(s). 