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Journal of Bacteriology, January 2005, p. 458-472, Vol. 187, No. 2
0021-9193/05/$08.00+0     doi:10.1128/JB.187.2.458-472.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

The LEE1 Promoters from both Enteropathogenic and Enterohemorrhagic Escherichia coli Can Be Activated by PerC-Like Proteins from Either Organism

Megan E. Porter,1* Paul Mitchell,1 Andrew Free,2 David G. E. Smith,1,{dagger} and David L. Gally1

Zoonotic and Animal Pathogens Research Laboratory, Medical Microbiology,1 Institute of Structural and Molecular Biology, University of Edinburgh, Edinburgh, United Kingdom2

Received 16 July 2004/ Accepted 6 October 2004

The PerC protein of enteropathogenic Escherichia coli (EPEC), encoded by the pEAF plasmid, is an activator of the locus of enterocyte effacement (LEE) pathogenicity island via the LEE1 promoter. It has been assumed that the related LEE-containing pathogen enterohemorrhagic E. coli (EHEC) lacks PerC-dependent activation due to utilization of an alternative LEE1 promoter and lack of a perC gene. However, we show here that EPEC PerC can activate both the EPEC and EHEC LEE1 promoters and that the major transcriptional start site is similarly located in both organisms. Moreover, a PerC-like protein family identified from EHEC genome analyses, PerC1 (also termed PchABC), can also activate both promoters in a manner similar to that of EPEC PerC. The perC1 genes are carried by lambdoid prophages, which exist in multiple copies in different EHEC strains, and have a variable flanking region which may affect their expression. Although individual perC1 copies appear to be poorly expressed, the total perC1 expression level from a strain encoding multiple copies approaches that of perC in EPEC and may therefore contribute significantly to LEE1 activation. Alignment of the protein sequences of these PerC homologues allows core regions of the PerC protein to be identified, and we show by site-directed mutagenesis that these core regions are important for function. However, purified PerC protein shows no in vitro binding affinity for the LEE1 promoter, suggesting that other core E. coli proteins may be involved in its mechanism of activation. Our data indicate that the nucleoid-associated protein IHF is one such protein.

* Corresponding author. Mailing address: Zoonotic and Animal Pathogens Research Laboratory, Medical Microbiology, University of Edinburgh, Teviot Place, Edinburgh, EH8 9AG, United Kingdom. Phone: 00 44 131 650 4522. Fax: 00 44 131 650 6531. E-mail: Megan.Porter{at}ed.ac.uk.

{dagger} Present address: Moredun Research Institute, Peniciuk, Midlothian, EH26 0PZ, United Kingdom.

Journal of Bacteriology, January 2005, p. 458-472, Vol. 187, No. 2
0021-9193/05/$08.00+0     doi:10.1128/JB.187.2.458-472.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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