Constituent of COPII-coated endoplasmic reticulum-derived transport vesicles. Required for efficient transport of a subset of secretory proteins to the Golgi. Associates with ERV25, ERP1 and ERP2. Interacts also with SAR1, SEC23 and SEC24. Recycles between endoplasmic reticulum and Golgi (PubMed:11560939). Present with 26800 molecules/cell in log phase SD medium. Belongs to the EMP24/GP25L family.