title: SecA interacts with ribosomes in order to facilitate posttranslational translocation in bacteria.
abstract: In Escherichia coli, translocation of exported proteins across the cytoplasmic membrane is dependent on the motor protein SecA and typically begins only after synthesis of the substrate has already been completed (i.e., posttranslationally). Thus, it has generally been assumed that the translocation machinery also recognizes its protein substrates posttranslationally. Here we report a specific interaction between SecA and the ribosome at a site near the polypeptide exit channel. This interaction is mediated by conserved motifs in SecA and ribosomal protein L23, and partial disruption of this interaction in vivo by introducing mutations into the genes encoding SecA or L23 affects the efficiency of translocation by the posttranslational pathway. Based on these findings, we propose that SecA could interact with its nascent substrates during translation in order to efficiently channel them into the "posttranslational" translocation pathway.
authors.affiliation: Center for Molecular Biology of the University of Heidelberg (ZMBH), ZMBH-DKFZ Alliance, Im Neuenheimer Feld 282, D-69120 Heidelberg, Germany.
authors.forename: Damon
authors.initials: D
authors.lastname: Huber
authors.forename: Nandhakishore
authors.initials: N
authors.lastname: Rajagopalan
authors.forename: Steffen
authors.initials: S
authors.lastname: Preissler
authors.forename: Mark A
authors.initials: MA
authors.lastname: Rocco
authors.forename: Frieder
authors.initials: F
authors.lastname: Merz
authors.forename: Günter
authors.initials: G
authors.lastname: Kramer
authors.forename: Bernd
authors.initials: B
authors.lastname: Bukau
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D017124:Conserved Sequence; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012270:Ribosomes / Q000378:metabolism*; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D016415:Sequence Alignment; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C497347:SecM protein, E coli; D014157:Transcription Factors; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins