Stabilizes the ATG5-ATG12 conjugate (By similarity). The ATG5-ATG12/ATG16 complex is required for efficient promotion of ATG8-conjugation to phosphatidylethanolamine and ATG8 localization to the pre-autophagosomal structure (PAS) (PubMed:26442587). Recruits also ATG3 to the PAS (By similarity). 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 (By similarity). Several units of each may be present in this complex (By similarity). Interacts directly with ATG12 (By similarity). Impairs the formation of preautophagosomal structures (PubMed:26442587). Kluyveromyces marxianus proteins are shorter in length and have a more ordered secondary structure than their S.cerevisiae counterparts, which might contribute to the superior thermotolerance and solubility (PubMed:26442587). K.marxianus could be therefore useful as a new model organism for further elucidation of the molecular details of autophagy (PubMed:26442587). Belongs to the ATG16 family.