Enables 1-phosphatidylinositol-3-kinase activity. Involved in several processes, including autophagosome assembly; phosphatidylinositol-mediated signaling; and response to leucine. Predicted to be located in several cellular components, including autolysosome; cytoplasmic vesicle; and midbody. Predicted to be part of phosphatidylinositol 3-kinase complex, class III, type I and phosphatidylinositol 3-kinase complex, class III, type II. Predicted to be active in several cellular components, including endosome; peroxisome; and phagophore assembly site. Orthologous to human PIK3C3 (phosphatidylinositol 3-kinase catalytic subunit type 3). [provided by Alliance of Genome Resources, Apr 2022]