Catalysis of the transfer of Atg12 to a substrate protein via the reaction X-Atg12 + S = X + S-Atg12, where X is either an E2 or E3 enzyme, the X-Atg12 linkage is a thioester bond, and the S-Atg12 linkage is an isopeptide bond between the C-terminal amino acid of Atg12 and the epsilon-amino group of lysine residues in the substrate.
E3