Constituent of COPII-coated endoplasmic reticulum-derived transport vesicles. Required for efficient transport of a subset of secretory proteins to the Golgi. The C-terminal di-lysine motif is required for exit from the endoplasmic reticulum. Required directly for packaging glycosylated pro-alpha-factor into COPII vesicles. Facilitates retrograde transport from the Golgi to the endoplasmic reticulum. The di-lysine motif confers endoplasmic reticulum localization for type I membrane proteins. Belongs to the SURF4 family.