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Journal of Bacteriology, October 2001, p. 5562-5570, Vol. 183, No. 19
Biocenter of the University of Würzburg
(Microbiology), Würzburg, Germany,1 and
Molecular Bacterial Pathogenesis Group, Veterinary Faculty,
Complutense University, 28040 Madrid, Spain2
Received 24 April 2001/Accepted 9 July 2001
Transcription factor PrfA controls the expression of virulence
genes essential for Listeria monocytogenes pathogenesis.
To gain insight into the structure-function relationship of PrfA, we
devised a positive-selection system to isolate mutations reducing or
abolishing transcriptional activity. The system is based on the
observation that the listerial iap gene, encoding the
p60 protein, is lethal if overexpressed in Bacillus
subtilis. A plasmid in which the iap gene is
placed under the control of the PrfA-dependent hly
promoter was constructed and introduced into B.
subtilis. This strain was rapidly killed when expression of
iap was induced by introduction of a second plasmid
carrying prfA. Two classes of B. subtilis
survivor mutants were identified: one carried mutations in
iap, and the second carried mutations in
prfA. Sequence analysis of the defective
prfA genes identified mutations in three regions of the
PrfA protein: region A, between amino acids 58 and 67 in the
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.19.5562-5570.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Positive Selection of Mutations Leading to Loss or
Reduction of Transcriptional Activity of PrfA, the Central Regulator of
Listeria monocytogenes Virulence

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domain of PrfA; region B, between amino acids 169 and 193, which
corresponds to the DNA-binding helix-turn-helix motif; and region C,
comprising the 38 C-terminal amino acids of PrfA, which form a leucine
zipper-like structure. PrfA proteins with mutations in regions B and C
were unable to bind to the PrfA-binding site in the target DNA, while
mutations in region A resulted in a protein still binding the target
DNA but unable to form a stable complex with RNA polymerase and
initiate transcription in vitro.
*
Corresponding author. Mailing address: Biocenter of the
University of Würzburg (Microbiology), Würzburg,
Germany. Phone: 49 931 8884401. Fax: 49 931 8884402. E-mail:
goebel{at}biozentrum.uni-wuerzburg.de.
Present address: Scientific Laboratories Products, Merck KGaA,
Darmstadt, Germany.
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