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Journal of Bacteriology, August 2009, p. 5180-5195, Vol. 191, No. 16
0021-9193/09/$08.00+0     doi:10.1128/JB.00476-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Sxy Induces a CRP-S Regulon in Escherichia coli{triangledown} ,{dagger}

Sunita Sinha,* Andrew D. S. Cameron,{ddagger} and Rosemary J. Redfield

Department of Zoology, University of British Columbia, Vancouver V6T 3Z4, Canada

Received 7 April 2009/ Accepted 1 June 2009

Escherichia coli is not considered naturally competent, yet it has homologues of the genes that most competent bacteria use for DNA uptake and processing. In Haemophilus influenzae and Vibrio cholerae, these genes are regulated by the Sxy and cyclic AMP receptor (CRP) proteins. We used microarrays to find out whether similar regulation occurs in E. coli. Expression of sxy strongly induced 63 transcriptional units, 34 of which required CRP for transcriptional activation and had promoter sites resembling the Sxy- and CRP-dependent CRP-S motif previously characterized in H. influenzae. As previously reported, sxy expression also induced the sigma-H regulon. Flagellar operons were downregulated by sxy expression, although motility remained unaffected. The CRP-S regulon included all of E. coli's known competence gene homologues, so we investigated Sxy's effect on competence-associated phenotypes. A sxy knockout reduced both "natural" plasmid transformation and competitive fitness in long-term culture. In addition, expression of plasmid-borne sxy led to production of type IV pilin, the main subunit of the DNA uptake machinery of most bacteria. Although H. influenzae Sxy only weakly activated the E. coli Sxy regulon, induction was dramatically improved when it was coexpressed with its cognate CRP, suggesting that intimate interactions between Sxy and CRP are required for transcriptional activation at CRP-S sites.

* Corresponding author. Mailing address: Department of Zoology, University of British Columbia, Life Sciences Center, Vancouver, Canada V6T 3Z4. Phone: (604) 822-6323. Fax: (604) 827-4135. E-mail: sinha{at}zoology.ubc.ca

{triangledown} Published ahead of print on 5 June 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: Department of Microbiology, Trinity College Dublin, Dublin 2, Ireland.

Journal of Bacteriology, August 2009, p. 5180-5195, Vol. 191, No. 16
0021-9193/09/$08.00+0     doi:10.1128/JB.00476-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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