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Journal of Bacteriology, March 2009, p. 1901-1909, Vol. 191, No. 6
0021-9193/09/$08.00+0     doi:10.1128/JB.01504-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

TtgV Represses Two Different Promoters by Recognizing Different Sequences{triangledown}

Sandy Fillet,1 Marisela Vélez,2 Duo Lu,3 Xiaodong Zhang,3 María-Trinidad Gallegos,1 and Juan L. Ramos1*

Department of Environmental Protection, EEZ-CSIC, Granada, Spain,1 Centro de Biología Molecular, Madrid, Spain,2 Imperial College, London, United Kingdom3

Received 24 October 2008/ Accepted 22 December 2008

Expression of the multidrug efflux pump ttgDEF and ttgGHI operons is modulated in vivo mainly by the TtgV repressor. TtgV is a multidrug recognition repressor that exhibits a DNA binding domain with a long interaction helix comprising residues 47 to 64. The pattern of expression of the two pumps is different in Pseudomonas putida: in the absence of effectors, the promoter for the ttgD gene is silent, whereas the ttgG gene is expressed at a high basal level. This correlates with the fact that TtgV exhibits a higher affinity for the ttgD operator (KD = 10 ± 1 nM) than for the ttgG (KD = 19 ± 1 nM) operator. Sequence analysis revealed that both operators are 40% identical, and mutational analysis of the ttgD and ttgG operators combined with electrophoretic mobility shift assays and in vivo expression analysis suggests that TtgV recognizes an inverted repeat with a high degree of palindromicity around the central axis. We generated a collection of alanine substitution mutants with substitutions between residues 47 and 64 of TtgV. The results of extensive combinations of promoter variants with these TtgV alanine substitution mutants revealed that TtgV modulates expression from ttgD and ttgG promoters through the recognition of both common and different sequences in the two promoters. In this regard, we found that TtgV mutants at residues 48, 50, 53, 54, 60, and 61 failed to bind ttgG but recognized the ttgD operator. TtgV residues R47, R52, L57, and T49 are critical for binding to both operators. Based on three-dimensional models, we propose that these residues contact nucleotides within the major groove of DNA.

* Corresponding author. Mailing address: Estación Experimental del Zaidín, C/ Profesor Albareda 1, E-18008 Granada, Spain. Phone: 34 958 181608. Fax: 34 958 135740. E-mail: jlramos{at}eez.csic.es

{triangledown} Published ahead of print on 29 December 2008.

Journal of Bacteriology, March 2009, p. 1901-1909, Vol. 191, No. 6
0021-9193/09/$08.00+0     doi:10.1128/JB.01504-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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