Ubiquitin-like protein involved in cytoplasm to vacuole transport (Cvt), autophagy vesicles formation, mitophagy, and nucleophagy. Conjugation with ATG5 through a ubiquitin-like conjugating system involving also ATG7 as an E1-like activating enzyme and ATG10 as an E2-like conjugating enzyme, is essential for its function. The ATG12-ATG5 conjugate functions as an E3-like enzyme which is required for lipidation of ATG8 and ATG8 association to the vesicle membranes. ATG12-ATG5 rearranges the association to the vesicle membranes (By similarity). Forms a conjugate with ATG5. Belongs to the ATG12 family. Extended N-terminus.