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Journal of Bacteriology, February 2007, p. 1407-1416, Vol. 189, No. 4
0021-9193/07/$08.00+0     doi:10.1128/JB.01036-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

CovR Activation of the Dipeptide Permease Promoter (PdppA) in Group A Streptococcus

Asiya A. Gusa, Barbara J. Froehlich, Devak Desai, Virginia Stringer, and June R. Scott^*

Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia 30322

Received 14 July 2006/ Accepted 11 September 2006

CovR, the two-component response regulator of Streptococcus pyogenes (group A streptococcus [GAS]) directly or indirectly represses about 15% of the genome, including genes encoding many virulence factors and itself. Transcriptome analyses also showed that some genes are activated by CovR. We asked whether the regulation by CovR of one of these genes, dppA, the first gene in an operon encoding a dipeptide permease, is direct or indirect. Direct regulation by CovR was suggested by the presence of five CovR consensus binding sequences (CBs) near the putative promoter. In this study, we identified the 5' end of the dppA transcript synthesized in vivo and showed that the start of dppA transcription in vitro is the same. We found that CovR binds specifically to the dppA promoter region (PdppA) in vitro with an affinity similar to that at which it binds to other CovR-regulated promoters. Disruption of any of the five CBs by a substitution of GG for TT inhibited CovR binding to that site in vitro, and binding at two of the CBs appeared cooperative. In vivo, CovR activation of transcription was not affected by individual mutations of any of the four CBs that we could study. This suggests that the binding sites are redundant in vivo. In vitro, CovR did not activate transcription from PdppA in experiments using purified GAS RNA polymerase and either linear or supercoiled DNA template. Therefore, we propose that in vivo, CovR may interfere with the binding of a repressor of PdppA.

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* Corresponding author. Mailing address: Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322. Phone: (404) 727-0402. Fax: (404) 727-8999. E-mail: scott{at}microbio.emory.edu.

Published ahead of print on 22 September 2006.

Present address: Medical College of Georgia, 1120 15th Street, Augusta, GA 30912.

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Journal of Bacteriology, February 2007, p. 1407-1416, Vol. 189, No. 4
0021-9193/07/$08.00+0     doi:10.1128/JB.01036-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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