Abstract
We have addressed the mechanism by which proteins are posttranslationally transported across the membrane of the yeast endoplasmic reticulum (ER). We demonstrate that BiP (Kar2p), a member of the Hsp70 family resident in the ER lumen, acts as a molecular ratchet during translocation of the secretory protein prepro-alpha factor through the channel formed by the Sec complex. Multiple BiP molecules associate with each translocation substrate following interaction with the J domain of the Sec63p component of the Sec complex. Bound BiP minimizes passive backward movements of the substrate through the channel, and BiP's subsequent dissociation results in a free polypeptide in the ER lumen. Antibodies against the substrate can replace BiP, indicating that a Brownian ratchet is sufficient to achieve translocation.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Cloning, Molecular
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Endoplasmic Reticulum / metabolism*
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Escherichia coli
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Fungal Proteins / chemistry
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Fungal Proteins / metabolism*
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HSP70 Heat-Shock Proteins / chemistry
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HSP70 Heat-Shock Proteins / metabolism*
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Intracellular Membranes / metabolism
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Kinetics
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Mating Factor
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Molecular Sequence Data
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Peptides / genetics
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Protein Binding
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Protein Biosynthesis
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Protein Precursors / metabolism*
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Protein Processing, Post-Translational*
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Recombinant Proteins / metabolism
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Saccharomyces cerevisiae / metabolism*
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Saccharomyces cerevisiae Proteins*
Substances
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Fungal Proteins
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HSP70 Heat-Shock Proteins
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KAR2 protein, yeast
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MF(ALPHA)1 protein, S cerevisiae
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Peptides
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Protein Precursors
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Recombinant Proteins
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Saccharomyces cerevisiae Proteins
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Mating Factor