Abstract
Vesicle budding from the endoplasmic reticulum (ER) has been reconstituted with washed membranes and three soluble proteins: Sec13 complex, Sec23 complex and the small GTPase Sar1p. The proteins that drive this cell‐free vesicle budding reaction form an ∼10 nm thick electron dense coat on ER‐derived vesicles. Although the overall mechanism of membrane budding driven by various cytoplasmic coats appears similar, the constituents of this new membrane coat are molecularly distinct from the non‐clathrin coat (COP) involved in intra‐Golgi transport and the clathrin‐containing coats. The new vesicle coat has been termed COPII.