Abstract
E. coli homologs of the signal recognition particle (SRP) and its receptor are essential for viability, but their role in protein export is unclear. To elucidate their function, we devised a genome-wide screen to identify genes that encode SRP substrates. Inhibition of the SRP pathway sharply blocked the membrane insertion of several polytopic inner membrane proteins (IMPs) that were predicted to be SRP substrates, but had a smaller effect on the insertion of other IMPs and no significant effect on preprotein translocation. Our results suggest that whereas most E. coli preproteins and some IMPs can utilize SRP-independent targeting pathways effectively, the structural features of a subset of IMPs have required the conservation of an SRP-based targeting machinery.
MeSH terms
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Bacterial Proteins / genetics
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Bacterial Proteins / metabolism*
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Biological Transport
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Escherichia coli / genetics
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Escherichia coli / metabolism*
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Escherichia coli Proteins*
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Genes, Bacterial
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Membrane Proteins / metabolism*
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Mutagenesis, Site-Directed
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Phenotype
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Protein Precursors / metabolism
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Receptors, Cytoplasmic and Nuclear / genetics
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Receptors, Cytoplasmic and Nuclear / metabolism*
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Signal Recognition Particle / genetics
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Signal Recognition Particle / metabolism*
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Transformation, Bacterial
Substances
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Bacterial Proteins
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Escherichia coli Proteins
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Ffh protein, E coli
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FtsY protein, Bacteria
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Membrane Proteins
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Protein Precursors
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Receptors, Cytoplasmic and Nuclear
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Recombinant Fusion Proteins
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Signal Recognition Particle