The function of RUBCNL (rubicon like autophagy enhancer, Ensembl gene identifier ENSG00000102445) is as follows. Regulator of autophagy that promotes autophagosome maturation by facilitating the biogenesis of phosphatidylinositol 3-phosphate (PtdIns(3)P) in late steps of autophagy (PubMed:28306502, PubMed:30704899). Acts by antagonizing RUBCN, thereby stimulating phosphatidylinositol 3-kinase activity of the PI3K/PI3KC3 complex (PubMed:28306502). 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 (PubMed:28306502). Binds phosphoinositides phosphatidylinositol 3-phosphate (PtdIns(3)P), 4- phosphate (PtdIns(4)P) and 5-phosphate (PtdIns(5)P) (PubMed:28306502). In addition to its role in autophagy, acts as a regulator of lipid and glycogen homeostasis (By similarity). May act as a tumor suppressor (Probable). {ECO:0000250|UniProtKB:Q3TD16, ECO:0000269|PubMed:28306502, ECO:0000269|PubMed:30704899, ECO:0000305|PubMed:23522960}.