Specific subunit of the TRAPP II complex, a highly conserved vesicle tethering complex that functions in the late Golgi as a guanine nucleotide exchanger (GEF) for the Golgi YPT1 GTPase. TRS120 plays a role in the YPT GEF activity of TRAPP II in concert with the two other TRAPP II-specific subunits TRS65 and TRS130. Part of the multisubunit TRAPP (transport protein particle) II complex composed of BET3, BET5, TRS20, TRS23, TRS31, TRS33, TRS65, TRS120 and TRS130. Interacts directly with TRS65. Present with 259 molecules/cell in log phase SD medium. Belongs to the TRS120 family.