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Helicobacter pylori FlgR Is an Enhancer-Independent Activator of ⁵⁴-RNA Polymerase Holoenzyme

Priyanka Brahmachary,¹ Mona G. Dashti,^1, Jonathan W. Olson,² and Timothy R. Hoover^1*

Department of Microbiology, University of Georgia, Athens, Georgia 30602,¹ Department of Microbiology, North Carolina State University, Raleigh, North Carolina 27695²

Received 9 January 2004/ Accepted 22 April 2004

Helicobacter pylori FlgR activates transcription with ⁵⁴-RNA polymerase holoenzyme (⁵⁴-holoenzyme) from at least five flagellar operons. Activators of ⁵⁴-holoenzyme generally bind enhancer sequences located >70 bp upstream of the promoter and contact ⁵⁴-holoenzyme bound at the promoter through DNA looping to activate transcription. H. pylori FlgR lacks the carboxy-terminal DNA-binding domain present in most ⁵⁴-dependent activators. As little as 42 bp of DNA upstream of the flaB promoter and 26 bp of DNA sequence downstream of the transcriptional start site were sufficient for efficient FlgR-mediated expression from a flaB'-'xylE reporter gene in H. pylori, indicating that FlgR does not use an enhancer to activate transcription. Other examples of ⁵⁴-dependent activators that lack a DNA-binding domain include Chlamydia trachomatis CtcC and activators from the other Chlamydia spp. whose genomes have been sequenced. FlgR from Helicobacter hepaticus and Campylobacter jejuni, which are closely related to H. pylori, appear to have carboxy-terminal DNA-binding domains, suggesting that the loss of the DNA-binding domain from H. pylori FlgR occurred after the divergence of these bacterial species. Removal of the amino-terminal regulatory domain of FlgR resulted in a constitutively active form of the protein that activated transcription from ⁵⁴-dependent genes in Escherichia coli. The truncated FlgR protein also activated transcription with E. coli ⁵⁴-holoenzyme in an in vitro transcription assay.

Present address: Department of Biological Sciences, Faculty of Science, University of Kuwait, Safat, Kuwait.

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