title: Binding protein BiP is required for translocation of secretory proteins into the endoplasmic reticulum in Saccharomyces cerevisiae.
abstract: The endoplasmic reticulum of mammalian cells contains a heat shock protein of approximately 70 kDa (hsp70) termed binding protein BiP that is thought to promote the folding and subunit assembly of newly synthesized proteins. To study BiP function, we placed the BiP-encoding gene from Saccharomyces cerevisiae under the control of a regulated promoter and examined the effects of BiP depletion. Reduction of BiP protein to about 15% of normal levels led to a profound reduction in secretion of alpha factor and invertase. At the same time, unglycosylated precursors of these proteins accumulated intracellularly. The predominant form of the invertase precursor had undergone signal sequence cleavage but accumulated as a soluble species in the cytosol. In contrast, the alpha-factor precursor was exclusively in the signal-uncleaved form. It sedimented with microsomal membranes and was exposed at the cytoplasmic face in a protease-resistant form. These findings suggest that, in yeast, BiP function is required for translocation of soluble proteins into the endoplasmic reticulum at a stage beyond the initial nascent chain-membrane association.
authors.affiliation: Department of Biochemistry, University of Toronto, Ontario, Canada.
authors.forename: T H
authors.initials: TH
authors.lastname: Nguyen
authors.forename: D T
authors.initials: DT
authors.lastname: Law
authors.forename: D B
authors.initials: DB
authors.lastname: Williams
mesh_terms: D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism*; D005800:Genes, Fungal; D006026:Glycoside Hydrolases / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism*; D000072235:Mating Factor; D010455:Peptides / Q000378:metabolism; D010675:Pheromones / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D043324:beta-Fructofuranosidase
chemical_list: D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C060153:KAR2 protein, yeast; D010455:Peptides; D010675:Pheromones; D000072235:Mating Factor; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase