title: The Brl domain in Sec63p is required for assembly of functional endoplasmic reticulum translocons.
abstract: Protein translocation into the endoplasmic reticulum occurs at pore-forming structures known as translocons. In yeast, two different targeting pathways converge at a translocation pore formed by the Sec61 complex. The signal recognition particle-dependent pathway targets nascent precursors co-translationally, whereas the Sec62p-dependent pathway targets polypeptides post-translationally. In addition to the Sec61 complex, both pathways also require Sec63p, an integral membrane protein of the Hsp40 family, and Kar2p, a soluble Hsp70 located in the ER lumen. Using a series of mutant alleles, we demonstrate that a conserved Brl (Brr2-like) domain in the COOH-terminal cytosolic region of Sec63p is essential for function both in vivo and in vitro. We further demonstrate that this domain is required for assembly of two oligomeric complexes of 350 and 380 kDa, respectively. The larger of these corresponds to the heptameric "SEC complex" required for post-translational translocation. However, the 350-kDa complex represents a newly defined hexameric SEC' complex comprising Sec61p, Sss1p, Sbh1p, Sec63p, Sec71p, and Sec72p. Our data indicate that the SEC' complex is required for co-translational protein translocation across the yeast ER membrane.
authors.affiliation: Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, United Kingdom.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Jermy
authors.forename: Martin
authors.initials: M
authors.lastname: Willer
authors.forename: Elaine
authors.initials: E
authors.lastname: Davis
authors.forename: Barrie M
authors.initials: BM
authors.lastname: Wilkinson
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Stirling
mesh_terms: D000483:Alleles; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000737:chemistry*; D047468:Immunoprecipitation; D026901:Membrane Transport Proteins / Q000737:chemistry*; D008861:Microsomes / Q000378:metabolism; D008957:Models, Genetic; D009841:Oligonucleotides / Q000737:chemistry; D011485:Protein Binding; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D020365:RNA Helicases; D012097:Repressor Proteins / Q000737:chemistry*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry*; D018271:Signal Recognition Particle
chemical_list: D005656:Fungal Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C060153:KAR2 protein, yeast; D026901:Membrane Transport Proteins; D009841:Oligonucleotides; D012097:Repressor Proteins; C074215:SEC63 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle; D004247:DNA; C104158:BRR2 protein, S cerevisiae; D020365:RNA Helicases