COPI

COPI is a coat system involved in retrieval toward the endoplasmic reticulum and traffic associated with the Golgi apparatus. Its coatomer assembly and ARF-family recruitment differ from COPII, while sharing membrane recruitment and cargo-selection principles.

Coatomer is a multisubunit protein complex that forms the COPI coat on transport carriers. With an ARF GTPase, it helps select cargo and deform membranes in traffic associated with the Golgi apparatus, including retrieval toward the endoplasmic reticulum. Coat assembly helps generate a carrier; later targeting and membrane fusion require additional machinery. Retrieval prevents forward traffic from progressively draining resident components from earlier compartments. ^[ref]