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 (By similarity). 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 (By similarity). 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 (PubMed:30704899). 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. Phosphorylated by MTOR at Ser-144 under nutrient-rich conditions. Phosphorylation prevents acetylation by KAT5/TIP60 and impairs RUBCNL/PACER function and autophagosome maturation. Under autophagy induction, Phosphorylation by MTOR is repressed, enabling acetylation by KAT5/TIP60. Acetylated by KAT5/TIP60 under autophagy induction, promoting autophagosome maturation and lipid metabolism (PubMed:30704899). Acetylation is prevented by phosphorylation by MTOR (By similarity). Lys-469 and Lys-559 constitute the key sites for tuning function in autophagy (By similarity). Mice display an increase in the ratio of liver to body weight and significantly lower total ketone bodies in the serum and liver after 24 hours of fasting (PubMed:30704899). Conditional deletion in the liver results in impaired autophagy flux, glycogen and lipid accumulation and liver fibrosis (PubMed:30704899).