title: A novel class of secA alleles that exert a signal-sequence-dependent effect on protein export in Escherichia coli.
abstract: The murine plasminogen activator inhibitor 2 (PAI2) signal sequence inefficiently promotes the export of E. coli alkaline phosphatase (AP). High-level expression of PAI2::AP chimeric proteins from the arabinose P(BAD) promoter is toxic and confers an Ara(S) phenotype. Most Ara(R) suppressors map to secA, as determined by sequencing 21 independent alleles. Mutations occur throughout the gene, including both nucleotide binding domains (NBDI and NBDII) and the putative signal sequence binding domain (SSBD). Using malE and phoA signal sequence mutants, we showed that the vast majority of these secA suppressors exhibit weak Sec phenotypes. Eight of these secA mutations were further characterized in detail. Phenotypically, these eight suppressors can be divided into three groups, each localized to one domain of SecA. Most mutations allow near-normal levels of wild-type preprotein export, but they enhance the secretion defect conferred by signal sequence mutations. Interestingly, one group exerts a selective effect on the export of PAI2::AP when compared to that of AP. In conclusion, this novel class of secA mutations, selected as suppressors of a toxic signal sequence, differs from the classical secA (prlD) mutations, selected as suppressors of defective signal sequences, although both types of mutations affect signal sequence recognition.
authors.affiliation: Department of Pathology, University of Geneva, Switzerland.
authors.forename: Karim
authors.initials: K
authors.lastname: Khatib
authors.forename: Dominique
authors.initials: D
authors.lastname: Belin
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001426:Bacterial Proteins; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000235:genetics / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D009154:Mutation; D033902:Periplasmic Binding Proteins / Q000235:genetics / Q000378:metabolism; D017396:Plasminogen Activator Inhibitor 2 / Q000235:genetics / Q000378:metabolism; D021382:Protein Sorting Signals / Q000235:genetics* / Q000502:physiology; D021381:Protein Transport / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D012641:Selection, Genetic
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; D026901:Membrane Transport Proteins; D033902:Periplasmic Binding Proteins; D017396:Plasminogen Activator Inhibitor 2; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D000069816:SEC Translocation Channels; D000469:Alkaline Phosphatase; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins