Molecular Cell
Volume 41, Issue 3, 4 February 2011, Pages 343-353
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Article
SecA Interacts with Ribosomes in Order to Facilitate Posttranslational Translocation in Bacteria

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Summary

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.

Highlights

► SecA binds directly to ribosomes near the polypeptide exit channel ► Binding involves conserved residues in ribosomal protein L23 and SecA ► Disruption of the SecA-ribosome interaction causes a protein translocation defect ► SecA binds with increased affinity specifically to ribosomes containing substrates

Cited by (0)

2

Present address: Department of Biology, University of Konstanz, D-78457 Konstanz, Germany

3

Present address: Department of Biomedical Engineering, Cornell University, Ithaca, NY 14853, USA

4

Present address: Molecular Partners AG, Wagistrasse 14, CH-8952 Schlieren-Zurich, Switzerland