Retention: some proteins are selectively excluded from COPII vesicles.

For retrograde transport from ERGIC and the cis-Golgi, COPI coated vesicles retrieve transport machinery, cargo receptors, lipid membrane, and escaped ER-resident proteins. Retrieved membrane proteins typically possess a C-terminal dilysine motif or a close variant. Retrieved soluble proteins typically have a C-terminal ‘KDEL’ motif.