prl mutations in the Escherichia coli secG gene.
SecG, an integral membrane component of the Escherichia coli preprotein translocase, contributes to the efficiency of the export process by undergoing cycles of topology inversion in the membrane, coupled with the insertion-deinsertion cycles of SecA. We have previously identified sec alleles of secG that cause a generalized secretion defect. In this study, by screening mutagenized secG libraries for suppressors of a malE signal sequence mutation, we isolated prl alleles of secG. By analogy with secY/prlA, secA/prlD, and secE/prlG, secG could therefore be called secG/prlH. The prlH mutations affect 13 codons distributed along the secG sequence, and none map to the codons affected by sec mutations. prlH suppressors suppress a variety of signal sequence mutations and they allow export of alkaline phosphatase lacking its entire signal sequence. Although secG was not identified in previous selections for prl mutants, several prlH alleles are as strong as the strongest known prlG alleles of secE. Some prlH alleles can also promote the export of alkaline phosphatase fused to predicted cytoplasmic domains of UhpT, an integral membrane protein. These results support the notion that SecG contributes to signal sequence recognition, and suggest that it may also contribute to the topology of integral membrane proteins.
Bost
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Département de Pathologie, Université de Genève, CH 1211 Geneva, Switzerland.
Belin
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D
D018528:ATP-Binding Cassette Transporters; D000469:Alkaline Phosphatase / Q000235:genetics; D000483:Alleles; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D002352:Carrier Proteins / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D009154:Mutation; D033902:Periplasmic Binding Proteins; D011498:Protein Precursors / Q000235:genetics; D021382:Protein Sorting Signals / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics; D000069816:SEC Translocation Channels
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D011498:Protein Precursors; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D000069816:SEC Translocation Channels; C088616:SecG protein, E coli; C461599:maltose transport system, E coli; D000469:Alkaline Phosphatase