Abstract
SOI3 was identified by a mutation, soi3-1, that suppressed a mutant trans-Golgi network (TGN) localization signal in the Kex2p cytosolic tail. SOI3, identical to RAV1, encodes a protein important for regulated assembly of vacuolar ATPase. Here, we show that Soi3/Rav1p is required for transport between the early endosome and the late endosome/prevacuolar compartment (PVC). By electron microscopy, soi3-1 mutants massively accumulated structures that resembled early endosomes. soi3Delta mutants exhibited a kinetic delay in transfer of the endocytic tracer dye FM4-64, from the 14 degrees C endocytic intermediate to the vacuole. The soi3Delta mutation delayed vacuolar degradation but not internalization of the a-factor receptor Ste3p. By density gradient fractionation, Soi3/Rav1p associated as a peripheral protein with membranes of a density characteristic of early endosomes. The soi3 null mutation markedly reduced the rate of Kex2p transport from the TGN to the PVC but had no effect on vacuolar protein sorting or cycling of Vps10p. These results suggest that assembly of vacuolar ATPase at the early endosome is required for transport of both Ste3p and Kex2p from the early endosome to the PVC and support a model in which cycling through the early endosome is part of the normal itinerary of Kex2p and other TGN-resident proteins.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Cation Transport Proteins / analysis
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Cation Transport Proteins / metabolism
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Cytoplasmic Vesicles / physiology*
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Endocytosis / genetics
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Endocytosis / physiology*
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Endosomes / physiology
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GTP-Binding Proteins / metabolism
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Membrane Proteins / analysis
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Membrane Proteins / genetics
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Membrane Proteins / metabolism*
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Membrane Proteins / physiology*
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Mutation / genetics
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Proprotein Convertases / genetics
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Proprotein Convertases / metabolism
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Protein Transport / genetics
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Protein Transport / physiology
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Receptors, G-Protein-Coupled / analysis
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Receptors, G-Protein-Coupled / metabolism
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Receptors, Mating Factor
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Receptors, Pheromone / analysis
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Receptors, Pheromone / metabolism
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Saccharomyces cerevisiae / genetics
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Saccharomyces cerevisiae / immunology
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Saccharomyces cerevisiae / physiology*
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Saccharomyces cerevisiae Proteins / analysis
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Saccharomyces cerevisiae Proteins / genetics
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Saccharomyces cerevisiae Proteins / metabolism*
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Saccharomyces cerevisiae Proteins / physiology*
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Sequence Deletion / genetics
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Vacuoles / immunology
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Vacuoles / physiology
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Vacuoles / ultrastructure
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Vesicular Transport Proteins / analysis
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Vesicular Transport Proteins / physiology
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trans-Golgi Network / physiology*
Substances
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Cation Transport Proteins
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Membrane Proteins
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PEP1 protein, S cerevisiae
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Receptors, G-Protein-Coupled
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Receptors, Mating Factor
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Receptors, Pheromone
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STE3 protein, S cerevisiae
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Saccharomyces cerevisiae Proteins
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Soi3 protein, S cerevisiae
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Vesicular Transport Proteins
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ZRT1 protein, S cerevisiae
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Proprotein Convertases
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KEX2 protein, S cerevisiae
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GTP-Binding Proteins
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VPS1 protein, S cerevisiae