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