Atg12 transferases catalyse the transfer of the ubiquitin-like protein Atg12 from one substrate to another. Analogous to ubiquitination, Atg12 is first activated by the E1-like enzyme Atg7, and is then transferred to the E2-like enzyme Atg10. Atg12 is eventually conjugated to the target protein Atg5, though there is no typical E3 enzyme involved in this process. Atg12 transferase activity is required for autophagosome biogenesis. (Adapted from PMID:18704115.)