Budding from Golgi membranes requires the coatomer complex of non-clathrin coat proteins.
Do the coats on vesicles budded from the Golgi apparatus actually cause the budding, or do they simply coat buds (Fig. 1)? One view (the membrane-mediated budding hypothesis) is that budding is an intrinsic property of Golgi membranes not requiring extrinsic coat proteins. Assembly of coats from dispersed subunits is super-imposed upon the intrinsic budding process and is proposed to convert the tips of tubules into vesicles. The alternative view (the coat-mediated budding hypothesis) is that coat formation provides the essential driving force for budding. The membrane-mediated budding hypothesis was inspired by the microtubule-dependent extension of apparently uncoated, 90-nm-diameter membrane tubules from the Golgi apparatus and other organelles in vivo after treatment with brefeldin A, a drug that inhibits the assembly of coat proteins onto Golgi membranes. This hypothesis predicts that tubules will be extended when coat proteins are unavailable to convert tubule-derived membrane into vesicles. Here we use a cell-free system in which coated vesicles are formed from Golgi cisternae to show that, on the contrary, when budding diminishes as a result of immunodepletion of coat protein pools, tubules are not formed at the expense of vesicles. We conclude that coat proteins are required for budding from Golgi membranes.
Orci
L
L
Institute of Histology and Embryology, University of Geneva Medical School, Switzerland.
Palmer
D J
DJ
Ravazzola
M
M
Perrelet
A
A
Amherdt
M
M
Rothman
J E
JE
D020727:ADP-Ribosylation Factors; D000818:Animals; D000911:Antibodies, Monoclonal; D002417:Cattle; D020756:Coatomer Protein; D019204:GTP-Binding Proteins / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D007425:Intracellular Membranes / Q000378:metabolism / Q000502:physiology*; D008099:Liver / Q000166:cytology; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism; D011485:Protein Binding; D011817:Rabbits
D000911:Antibodies, Monoclonal; D020756:Coatomer Protein; D046911:Macromolecular Substances; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D019204:GTP-Binding Proteins; D020727:ADP-Ribosylation Factors