title: The alternative sigma factor sigma28 of Legionella pneumophila restores flagellation and motility to an Escherichia coli fliA mutant.
abstract: Gene expression in Legionella pneumophila, the etiological agent of Legionnaires' disease, can be controlled by alternative forms of RNA polymerase programmed by distinct sigma factors. To understand the regulation of L. pneumophila flagellin expression, we cloned the sigma factor (FliA) of RNA polymerase responsible for the transcription of the flagellin gene, flaA. FliA is a member of the sigma28 class of alternative sigma factors identified in several bacterial genera. The gene fliA has been isolated from an expression library of L. pneumophila isolate Corby in Escherichia coli K-12. This library was transformed into a fliA mutant of E. coli K-12 containing a plasmid carrying the L. pneumophila-specific flaA promoter fused to the reporter gene luxAB. Screening the obtained transformants for luciferase activity, we isolated the major part of the fliA gene on a 1.64-kb fragment. This fragment was sequenced and used for reverse PCR in order to recover the complete fliA gene. The resulting 1.03-kb fragment was shown to contain the entire fliA gene. L. pneumophila FliA has 55 and 43% amino acid identity with the homologous sequences of Pseudomonas aeruginosa and E. coli. Furthermore, the L. pneumophila fliA gene was able to restore the flagellation and the motility defect of an E. coli fliA mutant. This result suggests that the L. pneumophila sigma28 protein can bind to the E. coli core RNA polymerase to direct transcription initiation from the flaA-specific promoter.
authors.affiliation: Institut für Molekulare Infektionsbiologie, Universität Würzburg, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Heuner
authors.forename: J
authors.initials: J
authors.lastname: Hacker
authors.forename: B C
authors.initials: BC
authors.lastname: Brand
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000502:physiology; D001483:Base Sequence; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics / Q000502:physiology; D005407:Flagella / Q000235:genetics*; D005408:Flagellin / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D005798:Genes, Bacterial / Q000235:genetics; D017930:Genes, Reporter / Q000235:genetics; D005816:Genetic Complementation Test; D016952:Legionella pneumophila / Q000235:genetics* / Q000502:physiology; D008156:Luciferases / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic / Q000235:genetics; D011993:Recombinant Fusion Proteins; D015183:Restriction Mapping; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012808:Sigma Factor / Q000235:genetics* / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; C064971:FliA protein, Bacteria; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; D005408:Flagellin; C067138:flaA protein, bacteria; D008156:Luciferases