Involved in ER to Golgi vesicle-mediated transport by either facilitating USO1-dependent and -independent tethering or increasing target accuracy of fusion events of COPII-coated vesicles. Interacts with GRH1 (via C-terminus), probably forming a heterooligomer consisting of a GRH1 dimer and a BUG1 dimer. Localizes to cytoplasm in a punctate pattern. Localizes to cis-Golgi together with GRH1. Present with 5220 molecules/cell in log phase SD medium.