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Journal of Bacteriology, November 1998, p. 5727-5732, Vol. 180, No. 21
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Transcriptional Regulation of the
Streptococcus mutans gal Operon by the GalR
Repressor
Dragana
Ajdi
and
Joseph J.
Ferretti*
Department of Microbiology and Immunology,
The University of Oklahoma Health Sciences Center, Oklahoma City,
Oklahoma 73104
Received 1 June 1998/Accepted 26 August 1998
The galactose operon of Streptococcus mutans is
transcriptionally regulated by a repressor protein (GalR) encoded by
the galR gene, which is divergently oriented from the
structural genes of the gal operon. To study the regulatory
function of GalR, we partially purified the protein and examined its
DNA binding activity by gel mobility shift and DNase I footprinting
experiments. The protein specifically bound to the
galR-galK intergenic region at an operator sequence, the
position of which would suggest that GalR plays a role in the
regulation of the gal operon as well as
autoregulation. To further examine this hypothesis, transcriptional start sites of the gal operon and the
galR gene were determined. Primer extension analysis showed
that both promoters overlap the operator, indicating that GalR most
likely represses transcription initiation of both promoters. Finally,
the results from in vitro binding experiments with potential effector
molecules suggest that galactose is a true intracellular inducer of the
galactose operon.
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, The University of Oklahoma, HSC, 940, S. L. Young Blvd., Oklahoma City, OK 73104. Phone: (405)
271-2332. Fax: (405) 271-3151. E-mail:
Joe-Ferretti{at}uokhsc.edu.
Journal of Bacteriology, November 1998, p. 5727-5732, Vol. 180, No. 21
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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