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Chlamydial GroEL Autoregulates Its Own Expression through Direct Interactions with the HrcA Repressor Protein

Department of Microbiology and Molecular Genetics,¹ Department of Medicine, School of Medicine, University of California, Irvine, California 92697-4025,² Department of Pharmacology, University of Colorado Health Sciences Center, Aurora, Colorado 80045,³ Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037⁴

Received 6 June 2005/ Accepted 24 August 2005

In the pathogenic bacterium Chlamydia trachomatis, a transcriptional repressor, HrcA, regulates the major heat shock operons, dnaK and groE. Cellular stress causes a transient increase in transcription of these heat shock operons through relief of HrcA-mediated repression, but the pathway leading to derepression is unclear. Elevated temperature alone is not sufficient, and it is hypothesized that additional chlamydial factors play a role. We used DNA affinity chromatography to purify proteins that interact with HrcA in vivo and identified a higher-order complex consisting of HrcA, GroEL, and GroES. This endogenous HrcA complex migrated differently than recombinant HrcA, but the complex could be disrupted, releasing native HrcA that resembled recombinant HrcA. In in vitro assays, GroEL increased the ability of HrcA to bind to the CIRCE operator and to repress transcription. Other chlamydial heat shock proteins, including the two additional GroEL paralogs present in all chlamydial species, did not modulate HrcA activity.

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