The PI(3,5)P2 regulatory complex regulates both the synthesis and turnover of phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P2). Catalyzes the phosphorylation of phosphatidylinositol 3-phosphate on the fifth hydroxyl of the myo-inositol ring, to form phosphatidylinositol 3,5-bisphosphate (By similarity). a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol-3-phosphate) + ATP = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol-3,5-bisphosphate) + ADP + H(+) Component of the PI(3,5)P2 regulatory complex at least composed of ATG18, SAC/FIG4, FAB1 and VAC14. Lacks the FYVE domain, necessary to efficiently target the protein to membranes containing the phosphatidylinositol-3P substrate. Therefore, its molecular function remains unknown.