COPI proteins: a model for their role in vesicle budding

COPI-coated vesicles are involved in intracellular trafficking between the endoplasmic reticulum and the Golgi complex. In the current model for COPI assembly the small GTP-binding protein ADP-ribosylation factor 1 is recruit ed from the cytoplasm to the Golgi membrane followed by binding of the hete ro-oligomeric protein complex coatomer. However, the mechanism of subsequen t vesicle budding is discussed controversially. This review summarizes the available experimental data on the COPI coat and discusses a model of how t he major coat protein, coatomer, might act in vesicle budding.