Component of the vacuole-localized DSC E3 ubiquitin ligase complex involved in the targeting of the complex to the vacuole membrane via the AP3 pathway to ubiquinate vacuolar membrane proteins (PubMed:29355480). Competes with GLD1 to determine the subcellular localizations of the DSC complex (PubMed:29355480). Part of the vacuole-localized DSC E3 ligase complex composed of at least TUL1, DSC2, DSC3, UBX3, CDC48 and VLD1.