TRAPP plays a key role in the late stages of endoplasmic reticulum to Golgi traffic. Part of the multisubunit TRAPP (transport protein particle) complex composed of bet3, bet5, trs20, trs23, trs31, trs33, trs65, trs85, trs120 and trs130. Belongs to the TRAPP small subunits family. BET3 subfamily.