E1-like activating enzyme involved in the 2 ubiquitin-like systems required for cytoplasm to vacuole transport (Cvt) and autophagy. Activates ATG12 for its conjugation with ATG5 and ATG8 for its conjugation with phosphatidylethanolamine. Both systems are needed for the ATG8 association to Cvt vesicles and autophagosomes. Involved in the senescence process (PubMed:12070171). Involved in the degradation of damaged peroxisomes (PubMed:24368788). Involved in the non-selective degradation of chlorophylls and photosynthetic proteins during stress-induced leaf yellowing (PubMed:24510943). Homodimer. Interacts with ATG8 through a thioester bond between Cys-558 and the C-terminal glycine of ATG8 and with ATG12 through a thioester bond between Cys-558 and the C-terminal glycine of ATG12. Interacts also with ATG3 (By similarity). Constitutively expressed (at protein level). Up-regulated during leaf senescence. The C-terminal residues are required for homodimerization, as well as the interactions with ATG3, ATG8 and ATG12. The GxGxxG motif is important for the function, possibly through binding with ATP. Increased number of peroxisomes and accumulation of peroxisomal proteins. Belongs to the ATG7 family.