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Journal of Bacteriology, January 2000, p. 57-66, Vol. 182, No. 1
0021-9193/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The VirR Response Regulator from Clostridium perfringens Binds Independently to Two Imperfect Direct Repeats Located Upstream of the pfoA Promoter

Jackie K. Cheung and Julian I. Rood*

Bacterial Pathogenesis Research Group, Department of Microbiology, Monash University, Clayton 3800, Australia

Received 21 July 1999/Accepted 7 October 1999

Regulation of toxin production in the gram-positive anaerobe Clostridium perfringens occurs at the level of transcription and involves a two-component signal transduction system. The sensor histidine kinase is encoded by the virS gene, while its cognate response regulator is encoded by the virR gene. We have constructed a VirR expression plasmid in Escherichia coli and purified the resultant His-tagged VirR protein. Gel mobility shift assays demonstrated that VirR binds to the region upstream of the pfoA gene, which encodes perfringolysin O, but not to regions located upstream of the VirR-regulated plc, colA, and pfoR genes, which encode alpha-toxin, collagenase, and a putative pfoA regulator, respectively. The VirR binding site was shown by DNase I footprinting to be a 52-bp core sequence situated immediately upstream of the pfoA promoter. When this region was deleted, VirR was no longer able to bind to the pfoA promoter. The binding site was further localized to two imperfect direct repeats (CCCAGTTNTNCAC) by site-directed mutagenesis. Binding and protection analysis of these mutants indicated that VirR had the ability to bind independently to the two repeated sequences. Based on these observations it is postulated that the VirR positively regulates the synthesis of perfringolysin O by binding directly to a region located immediately upstream of the pfoA promoter and activating transcription.

* Corresponding author. Mailing address: Bacterial Pathogenesis Research Group, Department of Microbiology, Monash University, Clayton 3800, Australia. Phone: 61 3 9905 4825. Fax: 61 3 9905 4811. E-mail: Julian.Rood{at}med.monash.edu.au.

Journal of Bacteriology, January 2000, p. 57-66, Vol. 182, No. 1
0021-9193/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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