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Journal of Bacteriology, December 2005, p. 8256-8266, Vol. 187, No. 24
0021-9193/05/$08.00+0     doi:10.1128/JB.187.24.8256-8266.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Characterization of the Detachable Rho-Dependent Transcription Terminator of the fimE Gene in Escherichia coli K-12

Paul Hinde, Padraig Deighan, and Charles J. Dorman^*

Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College, Dublin 2, Ireland

Received 27 June 2005/ Accepted 19 September 2005

The fim genetic switch in the chromosome of Escherichia coli K-12 is an invertible DNA element that harbors the promoter for transcription of the downstream fim structural genes and a transcription terminator that acts on the upstream fimE regulatory gene. Switches oriented appropriately for structural gene transcription also allow fimE mRNA to read through, whereas those in the opposite orientation terminate the fimE message. We show here that termination is Rho dependent and is suppressed in a rho mutant or by bicyclomycin treatment when fimE mRNA is expressed by the fimE gene, either from a multicopy recombinant plasmid or in its native chromosomal location. Two cis-acting elements within the central portion of the 314-bp invertible DNA switch were identified as contributors to Rho-dependent termination and dissected. These fim sequence elements show similarities to well-characterized Rho utilization (rut) sites and consist of a boxA motif and a C-rich and G-poor region of approximately 40 bp. Deletion of the boxA motif alone had only a subtle negative effect on Rho function. However, when this element was deleted in combination with the C-rich, G-poor region, Rho function was considerably decreased. Altering the C-to-G ratio in favor of G in this portion of the switch also strongly attenuated transcription termination. The implications of the existence of a fimE-specific Rho-dependent terminator within the invertible switch are discussed in the context of the fim regulatory circuit.

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* Corresponding author. Mailing address: Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College, Dublin 2, Ireland. Phone: 353 1 608 2013. Fax: 353 1 679 9294. E-mail: cjdorman{at}tcd.ie.

Present address: Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115.

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Journal of Bacteriology, December 2005, p. 8256-8266, Vol. 187, No. 24
0021-9193/05/$08.00+0     doi:10.1128/JB.187.24.8256-8266.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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