A Ypt/Rab effector complex containing the Sec1 homolog Vps33p is required for homotypic vacuole fusion.
Yeast vacuoles undergo priming, docking, and homotypic fusion, although little has been known of the connections between these reactions. Vacuole-associated Vam2p and Vam6p (Vam2/6p) are components of a 65S complex containing SNARE proteins. Upon priming by Sec18p/NSF and ATP, Vam2/6p is released as a 38S subcomplex that binds Ypt7p to initiate docking. We now report that the 38S complex consists of both Vam2/6p and the class C Vps proteins [Reider, S. E. and Emr, S. D. (1997) Mol. Biol. Cell 8, 2307-2327]. This complex includes Vps33p, a member of the Sec1 family of proteins that bind t-SNAREs. We term this 38S complex HOPS, for homotypic fusion and vacuole protein sorting. This unexpected finding explains how Vam2/6p associates with SNAREs and provides a mechanistic link of the class C Vps proteins to Ypt/Rab action. HOPS initially associates with vacuole SNAREs in "cis" and, after release by priming, hops to Ypt7p, activating this Ypt/Rab switch to initiate docking.
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Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755-3844, USA.
Eitzen
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Margolis
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Wickner
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Price
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D033942:Adaptor Proteins, Vesicular Transport; D000906:Antibodies / Q000494:pharmacology; D002352:Carrier Proteins / Q000145:classification / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D005656:Fungal Proteins / Q000145:classification / Q000378:metabolism*; D046911:Macromolecular Substances; D008561:Membrane Fusion / Q000187:drug effects; D008565:Membrane Proteins / Q000145:classification / Q000378:metabolism; D009687:Nuclear Proteins; D011233:Precipitin Tests; D011485:Protein Binding; D016601:RNA-Binding Proteins / Q000145:classification / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D050600:SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D014617:Vacuoles / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D033942:Adaptor Proteins, Vesicular Transport; D000906:Antibodies; D002352:Carrier Proteins; D005656:Fungal Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; C077734:NPL3 protein, S cerevisiae; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; C406817:VAM6 protein, S cerevisiae; C065454:VPS33 protein, S cerevisiae; C083878:VPS41 protein, S cerevisiae; D033921:Vesicular Transport Proteins; C079005:YPT7 protein, S cerevisiae; D020691:rab GTP-Binding Proteins