title: Organization of the yeast Golgi complex into at least four functionally distinct compartments.
abstract: Pro-alpha-factor (pro-alphaf) is posttranslationally modified in the yeast Golgi complex by the addition of alpha1,6-, alpha1,2-, and alpha1,3-linked mannose to N-linked oligosaccharides and by a Kex2p-initiated proteolytic processing event. Previous work has indicated that the alpha1,6- and alpha1,3-mannosylation and Kex2p-dependent processing of pro-alphaf are initiated in three distinct compartments of the Golgi complex. Here, we present evidence that alpha1,2-mannosylation of pro-alphaf is also initiated in a distinct Golgi compartment. Linkage-specific antisera and an endo-alpha1,6-D-mannanase (endoM) were used to quantitate the amount of each pro-alphaf intermediate during transport through the Golgi complex. We found that alpha1,6-, alpha1,2-, and alpha1,3-mannose were sequentially added to pro-alphaf in a temporally ordered manner, and that the intercompartmental transport factor Sec18p/N-ethylmaleimide-sensitive factor was required for each step. The Sec18p dependence implies that a transport event was required between each modification event. In addition, most of the Golgi-modified pro-alphaf that accumulated in brefeldin A-treated cells received only alpha1,6-mannosylation as did approximately 50% of pro-alphaf transported to the Golgi in vitro. This further supports the presence of an early Golgi compartment that houses an alpha1,6-mannosyltransferase but lacks alpha1,2-mannosyltransferase activity in vivo. We propose that the alpha1,6-, alpha1,2-, and alpha1,3-mannosylation and Kex2p-dependent processing events mark the cis, medial, trans, and trans-Golgi network of the yeast Golgi complex, respectively.
authors.affiliation: Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee 37235, USA.
authors.forename: W T
authors.initials: WT
authors.lastname: Brigance
authors.forename: C
authors.initials: C
authors.lastname: Barlowe
authors.forename: T R
authors.initials: TR
authors.lastname: Graham
mesh_terms: D000251:Adenosine Triphosphatases; D020126:Brefeldin A / Q000494:pharmacology; D004720:Endonucleases / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology; D005656:Fungal Proteins / Q000378:metabolism*; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism*; D008358:Mannose / Q000378:metabolism; D008364:Mannosyltransferases / Q000378:metabolism; D000072235:Mating Factor; D010455:Peptides / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins
chemical_list: D005656:Fungal Proteins; D010455:Peptides; D011498:Protein Precursors; D011500:Protein Synthesis Inhibitors; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D020126:Brefeldin A; D000072235:Mating Factor; C068701:KRE2 protein, S cerevisiae; D008364:Mannosyltransferases; C121563:alpha 1,3-mannosyltransferase; C058478:alpha 1,6-mannosyltransferase; D004720:Endonucleases; C117554:endonuclease M; D000251:Adenosine Triphosphatases; C064404:SEC18 protein, S cerevisiae; D008358:Mannose