FUNCTION: GABARAPL1 (GABARAPL2 or GABARAP or MAP1LC3)-modifier protein conjugating enzyme involved in its E2-like covalent binding to PE. ATG7 (E1-like enzyme) facilitates this reaction by forming an E1-E2 complex with ATG3 (E2-like enzyme). Preferred substrate is MAP1LC3A. Formation of the GABARAPL1-PE conjugate is essential for autophagy. SUBUNIT: Interacts with ATG7 and ATG12. The complex, composed of ATG3 and ATG7, plays a role in the conjugation of ATG12 to ATG5. SUBCELLULAR LOCATION: Cytoplasm. ALTERNATIVE PRODUCTS: 2 named isoforms produced by alternative splicing. TISSUE SPECIFICITY: Widely expressed, with a highest expression in heart, skeletal muscle, kidney, liver and placenta. SIMILARITY: Belongs to the ATG3 family.