Specific subunit of the TRAPP III complex that acts as an autophagy-specific guanine nucleotide exchange factor (GEF) for YPT1. TRS85 directs the TRAPP III complex to the phagophore assembly site (PAS) that is involved in autophagosome formation. Required for membrane expansion during autophagy and the CVT pathway. Required for sporulation. Has a role late in meiosis following DNA replication. Part of the multisubunit TRAPP (transport protein particle) III complex composed of BET3, BET5, TRS20, TRS23, TRS31, TRS33 and TRS85. Present with 8760 molecules/cell in log phase SD medium. Belongs to the TRS85 family.