Dephosphorylates a number of phosphatidylinositols (PIs) like phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2), but also phosphatidylinositol 3-phosphate (PtdIns(3)P), phosphatidylinositol 4-phosphate (PtdIns(4)P), and phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P2). Controls the cellular levels and subcellular distribution of phosphatidylinositol 3-phosphate and phosphatidylinositol 4,5-bisphosphate. Plays an essential role in a TGN (trans Golgi network)-to-early endosome pathway. Involved in clathrin-mediated protein sorting at the TGN. a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol-4,5-bisphosphate) + H2O = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol 4-phosphate) + phosphate Interacts with BSP1 and CHC1. Cytoplasmic punctate structures. Hyperosmotic stress causes translocation to actin patches. The SAC1 domain is capable of hydrolyzing phosphatidylinositol 3-phosphate (PtdIns(3)P), phosphatidylinositol 4-phosphate (PtdIns(4)P), and phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P2). The 5-phosphatase domain (residues 568 to 856) selectively removes the phosphate group at the 5' position of inositol of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). The C-terminal proline-rich domain is required for the function and associates with clathrin heavy chain CHC1. Present with 1520 molecules/cell in log phase SD medium. Belongs to the synaptojanin family. In the central section; belongs to the inositol 1,4,5-trisphosphate 5-phosphatase family.