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Journal of Bacteriology, February 2002, p. 760-770, Vol. 184, No. 3
0021-9193/01/$04.00+0     DOI: 10.1128/JB.184.3.760-770.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Integration of Global Regulation of Two Aromatic-Responsive {sigma}54-Dependent Systems: a Common Phenotype by Different Mechanisms

Chun Chau Sze, Lisandro M. D. Bernardo, and Victoria Shingler*

Department of Cell and Molecular Biology, Umeå University, S-901 87 Umeå, Sweden

Received 18 September 2001/ Accepted 8 November 2001

Pseudomonas-derived regulators DmpR and XylR are structurally and mechanistically related {sigma}54-dependent activators that control transcription of genes involved in catabolism of aromatic compounds. The binding of distinct sets of aromatic effectors to these regulatory proteins results in release of a repressive interdomain interaction and consequently allows the activators to promote transcription from their cognate target promoters. The DmpR-controlled Po promoter region and the XylR-controlled Pu promoter region are also similar, although homology is limited to three discrete DNA signatures for binding {sigma}54 RNA polymerase, the integration host factor, and the regulator. These common properties allow cross-regulation of Pu and Po by DmpR and XylR in response to appropriate aromatic effectors. In vivo, transcription of both the DmpR/Po and XylR/Pu regulatory circuits is subject to dominant global regulation, which results in repression of transcription during growth in rich media. Here, we comparatively assess the contribution of (p)ppGpp, the FtsH protease, and a component of an alternative phosphoenolpyruvate-sugar phosphotransferase system, which have been independently implicated in mediating this level of regulation. Further, by exploiting the cross-regulatory abilities of these two circuits, we identify the target component(s) that are intercepted in each case. The results show that (i) contrary to previous speculation, FtsH is not universally required for transcription of {sigma}54-dependent systems; (ii) the two factors found to impact the XylR/Pu regulatory circuit do not intercept the DmpR/Po circuit; and (iii) (p)ppGpp impacts the DmpR/Po system to a greater extent than the XylR/Pu system in both the native Pseudomonas putida and a heterologous Escherichia coli host. The data demonstrate that, despite the similarities of the specific regulatory circuits, the host global regulatory network latches onto and dominates over these specific circuits by exploiting their different properties. The mechanistic implications of how each of the host factors exerts its action are discussed.


* Corresponding author. Mailing address: Department of Cell and Molecular Biology, Umeå University, S-901 87 Umeå, Sweden. Phone: 46 90 7852534. Fax: 46 90 771420. E-mail: victoria.shingler{at}cmb.umu.se.


Journal of Bacteriology, February 2002, p. 760-770, Vol. 184, No. 3
0021-9193/01/$04.00+0     DOI: 10.1128/JB.184.3.760-770.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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