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Functional Analysis of the Heat Shock Regulator HrcA of Chlamydia trachomatis

Department of Microbiology and Molecular Genetics,¹ Department of Medicine, College of Medicine, University of California, Irvine, California 92697-4025²

Received 18 June 2002/ Accepted 27 August 2002

HrcA is a regulator of bacterial heat shock gene expression that binds to a cis-acting DNA element called CIRCE. It has been proposed that HrcA and CIRCE function as a repressor-operator pair. We have purified recombinant HrcA from the pathogenic bacterium Chlamydia trachomatis and have shown that it is a DNA-binding protein that functions as a negative regulator of transcription. HrcA bound specifically to the CIRCE element in a concentration-dependent manner. HrcA repressed the in vitro transcription of a chlamydial heat shock promoter, and this repression was promoter specific. HrcA-mediated repression appears to be dependent on the topological state of the promoter, as repression on a supercoiled promoter template was greater than that on a linearized template. These results provide direct support for the role of HrcA as a transcriptional repressor in bacteria. This is the first report of the in vitro reconstitution of transcriptional regulation in Chlamydia.

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