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Journal of Bacteriology, October 2008, p. 6419-6427, Vol. 190, No. 19
0021-9193/08/$08.00+0     doi:10.1128/JB.00431-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

DNA Supercoiling-Dependent Gene Regulation in Chlamydia{triangledown}

Eike Niehus,1 Eric Cheng,1 and Ming Tan1,2*

Department of Microbiology and Molecular Genetics,1 Department of Medicine, University of California, Irvine, California2

Received 27 March 2008/ Accepted 16 July 2008

The intracellular pathogen Chlamydia has an unusual developmental cycle marked by temporal expression patterns whose mechanisms of regulation are largely unknown. To examine if DNA topology can regulate chlamydial gene expression, we tested the in vitro activity of five chlamydial promoters at different superhelical densities. We demonstrated for the first time that individual chlamydial promoters show a differential response to changes in DNA supercoiling that correlates with the temporal expression pattern. The promoters for two midcycle genes, ompA and pgk, were responsive to alterations in supercoiling, and promoter activity could be regulated more than eightfold. In contrast, the promoters for three late transcripts, omcAB, hctA, and ltuB, were relatively insensitive to supercoiling, with promoter activity varying by no more than 2.2-fold over a range of superhelicities. To obtain a measure of how DNA supercoiling levels vary during the chlamydial developmental cycle, we recovered the cryptic chlamydial plasmid at different times after infection and assayed its superhelical density. The chlamydial plasmid was most negatively supercoiled at midcycle, with an approximate superhelical density of –0.07. At early and late times, the plasmid was more relaxed, with an approximate superhelicity of –0.03. Thus, we found a correlation between the responsiveness to supercoiling shown by the two midcycle promoters and the increased level of negative supercoiling during mid time points in the developmental cycle. Our results support a model in which the response of individual promoters to alterations in DNA supercoiling can provide a mechanism for global patterns of temporal gene expression in Chlamydia.

* Corresponding author. Mailing address: B240, Med Sci, Department of Microbiology & Molecular Genetics, University of California, Irvine, CA 92697-4025. Phone: (949) 824-3397. Fax: (949) 824-8598. E-mail: mingt{at}uci.edu

{triangledown} Published ahead of print on 25 July 2008.

Journal of Bacteriology, October 2008, p. 6419-6427, Vol. 190, No. 19
0021-9193/08/$08.00+0     doi:10.1128/JB.00431-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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