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Journal of Bacteriology, February 2009, p. 1056-1065, Vol. 191, No. 3
0021-9193/09/$08.00+0     doi:10.1128/JB.01436-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Transcription of clpP Is Enhanced by a Unique Tandem Repeat Sequence in Streptococcus mutans{triangledown}

Jiaqin Zhang,1,2,§ Anirban Banerjee,1,§,{dagger} and Indranil Biswas1*

Department of Microbiology, Molecular Genetics, and Immunology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, Kansas 66160,1 Department of Parasitology, Shandong University School of Medicine, 44# Wenhua Xi Road, Jinan, Shandong 250012, China2

Received 13 October 2008/ Accepted 20 November 2008

Streptococcus mutans, the primary causative agent of human dental caries, contains a single copy of the gene encoding ClpP, the chief intracellular protease responsible for tolerance to various environmental stresses. To better understand the role of ClpP in stress response, we investigated the regulation of clpP expression in S. mutans. Using semiquantitative reverse transcription-PCR analysis, we observed that, under nonstressed conditions, clpP expression is somewhat constant throughout the growth phases, although it gradually decreases as cells enter the late stationary phase. The half-life of the clpP transcript was found to be less than 1 minute. Sequence analysis of the clpP locus reveals the presence of a 50-bp tandem repeat sequence located immediately upstream of the clpP promoter (PclpP). PCR and DNA sequence analyses suggest that the number of tandem repeat units can vary from as few as two to as many as nine, depending on the particular S. mutans isolate. Further analysis, using a transcriptional reporter fusion consisting of PclpP fused to a promoterless gusA gene, indicates that the presence of the repeat sequence region within PclpP results in an approximately fivefold increase in expression from PclpP compared to the repeat-free transcriptional reporter fusion. CtsR, a transcriptional repressor that negatively regulates clpP expression, has no effect on this repeat-mediated induction of clpP transcription. Furthermore, the repeat sequence is not necessary for the induction of clpP under stress conditions. Database searches indicate that the region containing the tandem repeats is absent in the clpP loci in other bacteria, including other closely related Streptococcus spp., suggesting that the repeat sequences are specific for the induction of clpP expression in S. mutans. We speculate that a host-specific transcriptional activator might be involved in the upregulation of clpP expression in S. mutans.

* Corresponding author. Mailing address: 3025 Wahl Hall West, MS 3029, 3901 Rainbow Blvd., Kansas City, KS 66160. Phone: (913) 588-7019. Fax: (913) 588-7295. E-mail: ibiswas{at}kumc.edu

{triangledown} Published ahead of print on 1 December 2008.

§ These two authors contributed equally.

{dagger} Present address: Center for Microbial Sciences, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182.

Journal of Bacteriology, February 2009, p. 1056-1065, Vol. 191, No. 3
0021-9193/09/$08.00+0     doi:10.1128/JB.01436-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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