Abstract
COPII vesicle formation requires only three coat assembly subunits: Sar1p, Sec13/31p, and Sec23/24p. PI 4-phosphate or PI 4,5-bisphosphate is required for the binding of these proteins to liposomes. The GTP-bound form of Sar1p recruits Sec23/24p to the liposomes as well as to the ER membranes, and this Sar1p-Sec23/24p complex is required for the binding of Sec13/31p. Ultrastructural analysis shows that the binding of COPII coat proteins to liposomes results in coated patches, coated buds, and coated vesicles of 50-90 nm in diameter. Budding proceeds without rupture of the donor liposome or vesicle product. These observations suggest that the assembly of the COPII coat on the ER occurs by a sequential binding of coat proteins to specific lipids and that this assembly promotes the budding of COPII-coated vesicles.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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COP-Coated Vesicles
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Coated Vesicles / metabolism*
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Coated Vesicles / ultrastructure
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Endoplasmic Reticulum / metabolism
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Fungal Proteins / isolation & purification
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Fungal Proteins / metabolism*
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GTP-Binding Proteins / isolation & purification
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GTP-Binding Proteins / metabolism*
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GTPase-Activating Proteins
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Guanosine Monophosphate / analogs & derivatives
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Lipid Bilayers
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Liposomes / chemistry
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Liposomes / metabolism*
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Membrane Proteins / isolation & purification
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Membrane Proteins / metabolism*
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Microsomes / metabolism
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Monomeric GTP-Binding Proteins*
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Nuclear Pore Complex Proteins
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Phosphatidic Acids
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Phospholipids
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Proteolipids / metabolism
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Saccharomyces cerevisiae / metabolism
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Saccharomyces cerevisiae Proteins*
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Vesicular Transport Proteins
Substances
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Fungal Proteins
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GTPase-Activating Proteins
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Lipid Bilayers
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Liposomes
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Membrane Proteins
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Nuclear Pore Complex Proteins
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Phosphatidic Acids
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Phospholipids
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Proteolipids
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SEC13 protein, S cerevisiae
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SEC23 protein, S cerevisiae
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Saccharomyces cerevisiae Proteins
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Vesicular Transport Proteins
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proteoliposomes
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Guanosine Monophosphate
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GTP-Binding Proteins
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Monomeric GTP-Binding Proteins
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SAR1 protein, S cerevisiae