Involved in transport from the endoplasmic reticulum to the Golgi apparatus. Required to maintain SEC16A localization at discrete locations on the ER membrane perhaps by preventing its dissociation. SAR1A-GTP-dependent assembly of SEC16A on the ER membrane forms an organized scaffold defining endoplasmic reticulum exit sites (ERES) (By similarity). Interacts with B3GAT1. Belongs to the small GTPase superfamily. SAR1 family.