BiP and Sec63p are required for both co- and posttranslational protein translocation into the yeast endoplasmic reticulum.
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.
Brodsky
J L
JL
Department of Biological Sciences, University of Pittsburgh, PA 15260, USA.
Goeckeler
J
J
Schekman
R
R
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
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