title: Architecture of the protein-conducting channel associated with the translating 80S ribosome.
abstract: In vitro assembled yeast ribosome-nascent chain complexes (RNCs) containing a signal sequence in the nascent chain were immunopurified and reconstituted with the purified protein-conducting channel (PCC) of yeast endoplasmic reticulum, the Sec61 complex. A cryo-EM reconstruction of the RNC-Sec61 complex at 15.4 A resolution shows a tRNA in the P site. Distinct rRNA elements and proteins of the large ribosomal subunit form four connections with the PCC across a gap of about 10-20 A. Binding of the PCC influences the position of the highly dynamic rRNA expansion segment 27. The RNC-bound Sec61 complex has a compact appearance and was estimated to be a trimer. We propose a binary model of cotranslational translocation entailing only two basic functional states of the translating ribosome-channel complex.
authors.affiliation: Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA. roland.beckmann@charite.de
authors.forename: R
authors.initials: R
authors.lastname: Beckmann
authors.forename: C M
authors.initials: CM
authors.lastname: Spahn
authors.forename: N
authors.initials: N
authors.lastname: Eswar
authors.forename: J
authors.initials: J
authors.lastname: Helmers
authors.forename: P A
authors.initials: PA
authors.lastname: Penczek
authors.forename: A
authors.initials: A
authors.lastname: Sali
authors.forename: J
authors.initials: J
authors.lastname: Frank
authors.forename: G
authors.initials: G
authors.lastname: Blobel
mesh_terms: D001483:Base Sequence; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis; D012331:RNA, Fungal / Q000737:chemistry / Q000378:metabolism*; D012343:RNA, Transfer / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism / Q000648:ultrastructure*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D012331:RNA, Fungal; D012269:Ribosomal Proteins; D012343:RNA, Transfer