title: Signal sequence-independent membrane targeting of ribosomes containing short nascent peptides within the exit tunnel.
abstract: Ribosomes synthesizing inner membrane proteins in Escherichia coli are targeted to the translocon in the plasma membrane by the signal recognition particle (SRP) and the SRP receptor, FtsY. Here we show using a purified system that membrane targeting does not require an exposed signal-anchor sequence, as SRP-dependent targeting takes place with ribosomes containing short nascent peptides, with or without a signal-anchor sequence, within the peptide exit tunnel. Signaling from inside the tunnel involves ribosomal protein L23, which constitutes part of the SRP binding site. When nascent peptides emerge from the ribosome, the targeting complex is maintained with ribosomes exposing a signal-anchor sequence, whereas ribosomes exposing other sequences are released. These results indicate that ribosome-nascent chain complexes containing any nascent peptide within the exit tunnel can enter the SRP targeting pathway to be sorted at the membrane into ribosome-nascent chain complexes that synthesize either membrane or cytosolic proteins.
authors.affiliation: Institute of Molecular Biology, University of Witten/Herdecke, Stockumer Strasse 10, 55448 Witten, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Bornemann
authors.forename: Johannes
authors.initials: J
authors.lastname: Jöckel
authors.forename: Marina V
authors.initials: MV
authors.lastname: Rodnina
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wintermeyer
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D021381:Protein Transport; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D012269:Ribosomal Proteins / Q000737:chemistry; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment; D012697:Serine Endopeptidases / Q000378:metabolism; D018271:Signal Recognition Particle / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C087406:FtsY protein, Bacteria; D008565:Membrane Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D012269:Ribosomal Proteins; D018271:Signal Recognition Particle; C043816:ribosomal protein L23, E coli; D012697:Serine Endopeptidases; C026515:type I signal peptidase