Abstract
Two interacting heat shock cognate proteins in the lumen of the yeast endoplasmic reticulum (ER), Sec63p and BiP (Kar2p), are required for posttranslational translocation of yeast alpha-factor precursor in vitro. To investigate the role of these proteins in cotranslational translocation, we examined the import of invertase into wild-type, sec63, and kar2 mutant yeast membranes. We found that Sec63p and Kar2p are necessary for both co- and posttranslational translocation in yeast. Several kar2 mutants, one of which had normal ATPase activity, were defective in cotranslational translocation of invertase. We conclude that the requirement for BiP/Kar2p, which is not seen in a reaction reconstituted with pure mammalian membrane proteins [Görlich, D. & Rapoport, T.A. (1993) Cell 75, 615-630], is not due to a distinction between cotranslational translocation in mammalian cells and posttranslational translocation in yeast cells.
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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Biological Transport
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Endoplasmic Reticulum / metabolism*
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Fungal Proteins / genetics
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Fungal Proteins / metabolism*
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Glycoside Hydrolases / metabolism
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HSP70 Heat-Shock Proteins / genetics
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HSP70 Heat-Shock Proteins / metabolism*
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Heat-Shock Proteins*
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Membrane Proteins / genetics
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Membrane Proteins / metabolism*
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Membrane Transport Proteins*
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Microsomes / metabolism
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Models, Biological
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Mutation
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Protein Processing, Post-Translational*
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Saccharomyces cerevisiae / genetics
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Saccharomyces cerevisiae / metabolism*
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Saccharomyces cerevisiae Proteins*
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Subcellular Fractions / metabolism
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beta-Fructofuranosidase
Substances
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Fungal Proteins
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HSP70 Heat-Shock Proteins
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Heat-Shock Proteins
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KAR2 protein, yeast
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Membrane Proteins
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Membrane Transport Proteins
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SEC63 protein, S cerevisiae
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Saccharomyces cerevisiae Proteins
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Glycoside Hydrolases
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beta-Fructofuranosidase