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J. Bacteriol. doi:10.1128/JB.01213-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Cohabitation of two different lexA regulons in Pseudomonas putida

Departament de Genètica i Microbiologia, Universitat Autònoma de Barcelona 08193 Bellaterra, Spain; Centre de Recerca en Sanitat Animal (CReSA), 08193 Bellaterra, Spain; Biomedical Applications Group, Centro Nacional de Microelectrónica, CNM-IMB (CSIC), 08193 Bellaterra, Spain; Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología, CSIC, Campus de la Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain

^* To whom correspondence should be addressed. Email: jordi.barbe{at}uab.es.

	Abstract

In contrast with the vast majority of the Bacteria Domain members, several Pseudomonas and Xanthomonas species present two lexA genes whose products have been shown to recognize different LexA-binding motifs, making them an interesting target for the study of the interplay between cohabiting LexA regulons in a single species. Here we report the analysis of the genetic composition of the two LexA regulons of Pseudomonas putida KT2440 using a genomic micro-array. The data obtained indicate that one of the two LexA proteins (LexA1) seems to be in control of the conventional Escherichia coli-like SOS response, while the other LexA (LexA2) regulates only its own transcriptional unit, which includes the imuA, imuB and dnaE2 genes, and a gene (PP_3901) from a resident P. putida prophage. Furthermore, PP_3901 is also regulated by LexA1 and is required for DNA damage-mediated induction of several P. putida resident prophage genes. In silico searches suggest that this marked asymmetry in regulon contents is also the case for other Pseudomonas species presenting two lexA genes, and the implications of this asymmetry in the evolution of the SOS network are discussed.