Required for vacuolar protein sorting; may be required for the consumption of transport vesicles containing vacuolar protein precursors. May bind a Rab GTPase such as VPS21. Homodimer. The CUE domain (Coupling of ubiquitin conjugation to ER degradation) is monoubiquitin-binding and is required for intramolecular ubiquitination. Present with 4280 molecules/cell in log phase SD medium.