Involved in vesicular protein trafficking. Mainly functions in the early secretory pathway. Thought to act as cargo receptor at the lumenal side for incorporation of secretory cargo molecules into transport vesicles and to be involved in vesicle coat formation at the cytoplasmic side (By similarity). Probably oligomerizes with other members of the EMP24/GP25L family (By similarity). Associates with the COPI vesicle coat (coatomer). Associates with the COPII vesicle coat (coatomer). Cycles between the endoplasmic reticulum and Golgi via COPI and COPII dependent pathways. Mainly located in endoplasmic reticulum. The cytoplasmic C-terminal domain contains a functional dilysine-retrieval motif, which is involved in the retrograde Golgi-to-ER transport of the protein. Belongs to the EMP24/GP25L family.