Stabilizes the atg5-atg12 conjugate 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 pre-autophagosomal structure (PAS). Recruits also ATG3 to the PAS. Involved in endoplasmic reticulum-specific autophagic process and is essential for the survival of cells subjected to severe ER stress (By similarity). Homodimer (By similarity). Part of the atg5-atg12/atg16 complex. Several units of each may be present in this complex (By similarity). Belongs to the ATG16 family.