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Applied and Environmental Microbiology, September 2005, p. 5411-5419, Vol. 71, No. 9
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.9.5411-5419.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Dual Role of Response Regulator StyR in Styrene Catabolism Regulation

Livia Leoni, Giordano Rampioni, Valeria Di Stefano,{dagger} and Elisabetta Zennaro*

Department of Biology, University "Roma Tre," Viale G. Marconi 446, 00146 Rome, Italy

Received 27 January 2005/ Accepted 23 March 2005

In Pseudomonas fluorescens ST, the promoter of the styrene catabolic operon, PstyA, is induced by styrene and repressed by the addition of preferred carbon sources. PstyA is regulated by the StyS/StyR two-component system. The integration host factor (IHF) also plays a positive role in PstyA regulation. Three distinct StyR binding sites, which have different affinities for this response regulator, have been characterized on PstyA. The high-affinity StyR binding site (STY2) is necessary for promoter activity. The DNA region upstream of STY2 contains a lower-affinity StyR binding site, STY1, that partially overlaps the IHF binding site. Deletion of this region, designated URE (upstream regulatory element), has a dual effect on the PstyA promoter, decreasing the styrene-dependent activity and partially relieving the glucose repression. The lowest-affinity StyR binding site (STY3) is located downstream of the transcription start point. Deletion of the URE region and inactivation of the STY3 site completely abolished glucose-mediated repression of PstyA. In the proposed model StyR can act either as an activator or as a repressor, depending on which sites it occupies in the different growth conditions. We suggest that the cellular levels of phosphorylated StyR, as determined by StyS sensor kinase activity, and the interplay of this molecule with IHF modulate the activity of the promoter in different growth conditions.

* Corresponding author. Mailing address: Department of Biology, University "Roma Tre," Viale G. Marconi 446, 00146 Rome, Italy. Phone: (39) 06 55176318. Fax: (39) 06 55176321. E-mail: zennaro{at}bio.uniroma3.it.

{dagger} Present address: Department of Experimental Oncology, Molecular Oncogenesis Laboratory, Regina Elena Cancer Institute, Via delle Messi d'Oro 156, 00158 Rome, Italy.

Applied and Environmental Microbiology, September 2005, p. 5411-5419, Vol. 71, No. 9
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.9.5411-5419.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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