Autophagy factor required for autophagosome formation. Stabilizes ATG13, protecting it from proteasomal degradation. Interacts with ATG13 (PubMed:19287211, PubMed:19597335, PubMed:26299944). Associates with a complex composed of ATG13, ULK1 and RB1CC1; the association with this complex requires the presence of ATG13 (PubMed:19287211, PubMed:19597335). Under starvation conditions, it is localized to puncate structures primarily representing the isolation membrane; the isolation membrane sequesters a portion of the cytoplasm resulting in autophagosome formation. Belongs to the ATG101 family.