Regulator of autophagy that promotes autophagosome maturation by facilitating the biogenesis of phosphatidylinositol 3-phosphate (PtdIns(3)P) in late steps of autophagy. Acts by antagonizing RUBCN, thereby stimulating phosphatidylinositol 3-kinase activity of the PI3K/PI3KC3 complex. Following anchorage to the autophagosomal SNARE STX17, promotes the recruitment of PI3K/PI3KC3 and HOPS complexes to the autophagosome to regulate the fusion specificity of autophagosomes with late endosomes/lysosomes. Binds phosphoinositides phosphatidylinositol 3-phosphate (PtdIns(3)P), 4-phosphate (PtdIns(4)P) and 5-phosphate (PtdIns(5)P) (By similarity). In addition to its role in autophagy, acts as a regulator of lipid and glycogen homeostasis (By similarity). May act as a tumor suppressor (By similarity). Interacts with UVRAG; the interaction is direct and promotes association with the PI3K/PI3KC3 and HOPS complexes. Interacts with STX17. Associates with late autophagic structure. Recruitment to autophagosome membrane is promoted by autophagic stimuli. Acetylated by KAT5/TIP60 under autophagy induction, promoting autophagosome maturation and lipid metabolism. Lys-484 and Lys-574 constitute the key sites for tuning function in autophagy.