title: BiP and Sec63p are required for both co- and posttranslational protein translocation into the yeast endoplasmic reticulum.
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.
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, PA 15260, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Brodsky
authors.forename: J
authors.initials: J
authors.lastname: Goeckeler
authors.forename: R
authors.initials: R
authors.lastname: Schekman
mesh_terms: D001692:Biological Transport; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008861:Microsomes / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013347:Subcellular Fractions / Q000378:metabolism; D043324:beta-Fructofuranosidase
chemical_list: D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C060153:KAR2 protein, yeast; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C074215:SEC63 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase