title: Mammalian Sec61 is associated with Sec62 and Sec63.
abstract: In yeast, efficient protein transport across the endoplasmic reticulum (ER) membrane may occur co-translationally or post-translationally. The latter process is mediated by a membrane protein complex that consists of the Sec61p complex and the Sec62p-Sec63p subcomplex. In contrast, in mammalian cells protein translocation is almost exclusively co-translational. This transport depends on the Sec61 complex, which is homologous to the yeast Sec61p complex and has been identified in mammals as a ribosome-bound pore-forming membrane protein complex. We report here the existence of ribosome-free mammalian Sec61 complexes that associate with two ubiquitous proteins of the ER membrane. According to primary sequence analysis both proteins display homology to the yeast proteins Sec62p and Sec63p and are therefore named Sec62 and Sec63, respectively. The probable function of the mammalian Sec61-Sec62-Sec63 complex is discussed with respect to its abundance in ER membranes, which, in contrast to yeast ER membranes, apparently lack efficient post-translational translocation activity.
authors.affiliation: Universität Göttingen, Zentrum Biochemie und Molekulare Zellbiologie, Biochemie II, Heinrich-Düker-Weg 12, Göttingen 37073, Germany.
authors.forename: H A
authors.initials: HA
authors.lastname: Meyer
authors.forename: H
authors.initials: H
authors.lastname: Grau
authors.forename: R
authors.initials: R
authors.lastname: Kraft
authors.forename: S
authors.initials: S
authors.lastname: Kostka
authors.forename: S
authors.initials: S
authors.lastname: Prehn
authors.forename: K U
authors.initials: KU
authors.lastname: Kalies
authors.forename: E
authors.initials: E
authors.lastname: Hartmann
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001692:Biological Transport; D003001:Cloning, Molecular; D017931:DNA Primers; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D000069816:SEC Translocation Channels; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D005656:Fungal Proteins; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C499383:SEC61 protein, S cerevisiae; C074213:SEC62 protein, S cerevisiae; C074215:SEC63 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins