FUNCTION: Functions as an E1 enzyme essential for multisubstrates such as GABARAPL1 and ATG12. Forms intermediate conjugates with GABARAPL1 (GABARAPL2, GABARAP or MAP1ALC3). Formation of the final GABARAPL1-PE conjugate is essential for autophagy. SUBUNIT: Homodimer (By similarity). Interacts with ATG3 and ATG12. The complex, composed of ATG3 and ATG7, plays a role in the conjugation of ATG12 to ATG5. SUBCELLULAR LOCATION: Cytoplasm (Probable). ALTERNATIVE PRODUCTS: 2 named isoforms produced by alternative splicing. TISSUE SPECIFICITY: Widely expressed, especially in kidney, liver, lymph nodes and bone marrow. DOMAIN: The C-terminal part of the protein is essential for the dimerization and interaction with ATG3 and ATG12. SIMILARITY: Belongs to the ATG7 family. In yeast, ATG7 appears to be required for fusion of peroxisomal and vaculuolar membranes.