Constituent of COPII-coated endoplasmic reticulum-derived transport vesicles. Required for efficient transport of a subset of secretory proteins to the Golgi. Possesses a C-terminal dilysine motif that interacts with COPI coat subunits. Facilitates retrograde transport from the Golgi to the endoplasmic reticulum. Associates with EMP24, ERP1 and ERP2. Recycles between endoplasmic reticulum and Golgi. Present with 51700 molecules/cell in log phase SD medium. Belongs to the EMP24/GP25L family.