COPS REGULATING MEMBRANE TRAFFIC

Cytosolic coat proteins (COPs) regulate membrane traffic in eukaryotic cells. Three classes of coat protein complexes have so far been ident ified: clathrin and its adaptor proteins, coatomer (COPI), and COPII. Coatomer (composed of seven different subunits) and ADP-ribosylation f actor (ARF), which form the COPI coat, are required for budding of coa ted vesicles from membranes. COPI has been implicated in several steps of transport from the intermediate compartment to the cis-Golgi netwo rk, through cisternae of the Golgi stack, and is essential for retriev al to the endoplasmic reticulum (ER) of membrane proteins containing t he carboxy-terminal dilysine ER-retention motif. A family of structura lly and functionally related COPs may regulate all membrane traffic st eps in eukaryotic cells.