title: Exclusion of golgi residents from transport vesicles budding from Golgi cisternae in intact cells.
abstract: A central feature of cisternal progression/maturation models for anterograde transport across the Golgi stack is the requirement that the entire population of steady-state residents of this organelle be continuously transported backward to earlier cisternae to avoid loss of these residents as the membrane of the oldest (trans-most) cisterna departs the stack. For this to occur, resident proteins must be packaged into retrograde-directed transport vesicles, and to occur at the rate of anterograde transport, resident proteins must be present in vesicles at a higher concentration than in cisternal membranes. We have tested this prediction by localizing two steady-state residents of medial Golgi cisternae (mannosidase II and N-acetylglucosaminyl transferase I) at the electron microscopic level in intact cells. In both cases, these abundant cisternal constituents were strongly excluded from buds and vesicles. This result suggests that cisternal progression takes place substantially more slowly than most protein transport and therefore is unlikely to be the predominant mechanism of anterograde movement.
authors.affiliation: Department of Morphology, University of Geneva Medical School, 1211 Geneva 4, Switzerland.
authors.forename: L
authors.initials: L
authors.lastname: Orci
authors.forename: M
authors.initials: M
authors.lastname: Amherdt
authors.forename: M
authors.initials: M
authors.lastname: Ravazzola
authors.forename: A
authors.initials: A
authors.lastname: Perrelet
authors.forename: J E
authors.initials: JE
authors.lastname: Rothman
mesh_terms: D029681:Arabidopsis Proteins; D002352:Carrier Proteins / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000201:enzymology / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000201:enzymology* / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D007425:Intracellular Membranes / Q000201:enzymology* / Q000648:ultrastructure; D007515:Islets of Langerhans / Q000378:metabolism* / Q000648:ultrastructure; D008361:Mannosidases / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D017351:N-Acetylglucosaminyltransferases / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D010940:Plant Proteins; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases; D017351:N-Acetylglucosaminyltransferases; C024850:alpha-1,3-mannosyl-glycoprotein beta-1,2-N-acetylglucosaminyltransferase I; D008361:Mannosidases; C038829:mannosyl-oligosaccharide 1,3 - 1,6-alpha-mannosidase