Stabilizes the atg5-atg12 conjugate and mediates the formation of the 350 kDa complex, which is necessary for autophagy. The atg5-atg12/atg16 complex is required for efficient promotion of atg8-conjugation to phosphatidylethanolamine and atg8 localization to the preautophagosomal structure (PAS). Involved in endoplasmic reticulum-specific autophagic process and is essential for the survival of cells subjected to severe ER stress. Required for meiotic chromosome segregation. Homodimer (By similarity). Interacts with atg5. Impairs atg8-processing. Belongs to the ATG16 family.