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J. Bacteriol., 01 1997, 17-23, Vol 179, No. 1
K Heuner, J Hacker and BC Brand
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.
Copyright © 1997, American Society for Microbiology
The alternative sigma factor sigma28 of Legionella pneumophila restores flagellation and motility to an Escherichia coli fliA mutant
Institut fur Molekulare Infektionsbiologie, Universitat Wurzburg, Germany.
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