Required for protein transport through the secretory pathway. Probably involved in regulation of secretory vesicle formation at the trans-Golgi compartment. Mediates the proper polarized localization of SEC2, a GEF for SEC4, but does not alter the exchange activity of SEC2 on SEC4. Plays a role in autophagy. Alternates between an inactive form bound to GDP and an active form bound to GTP. Activated by the guanine nucleotide-exchange factor (GEF) TRAPP complex, and inactivated by GTPase-activating protein (GAP) GYP3. Interacts with YIF1, YIP3, YIP4 and YIP5. Interacts with the GEF SEC2. Interacts with TRS130. Present with 4298 molecules/cell in log phase SD medium. Belongs to the small GTPase superfamily. Rab family.