GTPase-activating protein (GAP) for ADP ribosylation factor 1 (ARF1). Implicated in coatomer-mediated protein transport between the Golgi complex and the endoplasmic reticulum. Hydrolysis of ARF1-bound GTP may lead to dissociation of coatomer from Golgi-derived membranes to allow fusion with target membranes (By similarity). Interacts with the coatomer complex. Interacts with C-terminal appendage domain of COPG1 (By similarity). Also found on peripheral punctate structures likely to be endoplasmic reticulum-Golgi intermediate compartment.