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Journal of Bacteriology, September 1999, p. 5373-5383, Vol. 181, No. 17
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Regulation of mga Transcription in the Group A Streptococcus: Specific Binding of Mga within Its Own Promoter and Evidence for a Negative Regulator

Kevin S. McIver,dagger Alec S. Thurman, and June R. Scott*

Department of Microbiology and Immunology, Rollins Research Center, Emory University, Atlanta, Georgia 30322

Received 22 April 1999/Accepted 25 June 1999

Transcription of mga, encoding the multiple virulence gene regulator of the group A streptococcus, is positively autoregulated. This regulation requires a DNA region (Pmga) that contains both a promoter proximal to mga (P2) and a promoter located further upstream (P1). To determine if Mga has a direct role in this process, its ability to bind to specific sequences within Pmga was tested. A purified fusion of Mga to the C-terminal end of maltose-binding protein (MBP-Mga), encoded by malE-mga, was shown previously to bind to the promoter regions of Mga-regulated genes, including scpA and emm. We report here that MBP-Mga can function in vivo to regulate emm and mga. Electrophoretic mobility shift assays and DNase I footprinting were used to demonstrate specific binding of MBP-Mga to two ca. 59-bp binding sites in Pmga centered around bases -108 and -180 from the major P2 start of transcription. Mga binding sites from Pemm and PscpA were shown to compete for binding at the two Pmga sites, suggesting that the same domain of Mga interacts at all of these promoter targets. Deletion of the distal Pmga binding site (site I) in vivo resulted in loss of Mga-dependent transcription from the P2 start. However, the same lesion resulted in an increase in P1 transcription that was independent of Mga. This suggests the existence of a repressor of mga transcription with a binding site overlapping those of Mga.

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

dagger Present address: Department of Microbiology, The University of Texas Southwestern Medical Center, Dallas, TX 75325-9048.

Journal of Bacteriology, September 1999, p. 5373-5383, Vol. 181, No. 17
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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