Polar transmembrane domains target proteins to the interior of the yeast vacuole.
Membrane proteins transported to the yeast vacuole can have two fates. Some reach the outer vacuolar membrane, whereas others enter internal vesicles, which form in late endosomes, and are ultimately degraded. The vacuolar SNAREs Nyv1p and Vam3p avoid this fate by using the AP-3-dependent pathway, which bypasses late endosomes, but the endosomal SNARE Pep12p must avoid it more directly. Deletion analysis revealed no cytoplasmic sequences necessary to prevent the internalization of Pep12p in endosomes. However, introduction of acidic residues into the cytoplasmic half of the transmembrane domain created a dominant internalization signal. In other contexts, this same feature diverted proteins from the Golgi to endosomes and slowed their exit from the endoplasmic reticulum. The more modestly polar transmembrane domains of Sec12p and Ufe1p, which normally serve to hold these proteins in the endoplasmic reticulum, also cause Pep12p to be internalized, as does that of the vacuolar protein Cps1p. It seems that quality control mechanisms recognize polar transmembrane domains at multiple points in the secretory and endocytic pathways and in endosomes sort proteins for subsequent destruction in the vacuole. These mechanisms may minimize the damaging effects of abnormally exposed polar residues while being exploited for the localization of some normal proteins.
Reggiori
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Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 2QH, United Kingdom.
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Pelham
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D000595:Amino Acid Sequence; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D021382:Protein Sorting Signals; D021381:Protein Transport; D050765:Qa-SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; D014617:Vacuoles / Q000378:metabolism*; D015003:Yeasts / Q000378:metabolism*
D005656:Fungal Proteins; D020662:Guanine Nucleotide Exchange Factors; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C081224:PEP12 protein, S cerevisiae; D021382:Protein Sorting Signals; D050765:Qa-SNARE Proteins; C071239:SEC12 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C103868:UFE1 protein, S cerevisiae; C107706:VAM3 protein, S cerevisiae