Also isolated in the Tn5 screen that yielded the constitutively a

Also isolated in the Tn5 screen that yielded the constitutively activated exopolysaccharide overproducing exoS mutant was a mutant of exoR[9]. Evidence has been provided to suggest a direct interaction

of ExoR with ExoS in the periplasm, with ExoR binding contributing to the maintenance of ExoS in an inactive conformation [13]. Furthermore, it has been proposed that cleavage of ExoR is induced by some yet unknown environmental signal during infection of the host plant, and this might modulate its ability to bind ExoS [14], resulting in its activation and regulation of the target genes. The exoS gene is situated within an operon along with hprK, part of an incomplete phosphotransferase BTK inhibitor system (PTS) in Alphaproteobacteria. In S. meliloti, HprK is involved in succinate mediated catabolite repression [15]. The establishment of a direct functional or regulatory link between the incomplete PTS and the ExoS/ChvI TCRS has been elusive, partly selleck chemicals llc because the systems have often been studied in isolation. Given the pleotropic nature of the exoS and chvI null mutants [10], investigation of gene expression using transcriptomics and proteomics might prove less than satisfactory, as the expression of many genes that are not direct regulatory targets is likely to be altered due to physiological changes in the cell. Indeed transcriptomics have identified hundreds

of genes whose expression is affected by the exoS96::Tn5 mutation [16]. Comparison of transcriptomes from two different chvI mutant strains (gain-of-function versus reduced-function) narrowed the set of genes regulated by ChvI and subsequently facilitated the selleck products identification by gel shift assays of three intergenic regions binding ChvI [17] and the determination of an 11-bp-long putative ChvI binding motif. However, for the majority of genes identified as being differentially expressed

in a ChvI dependent manner in that study, including the succinoglycan synthesis genes, no binding to upstream regions could be demonstrated. As an alternative, we applied a method to screen for DNA fragments that were directly bound by the ChvI transcriptional regulator. Analysis of these targets suggests important metabolic pathways affected by ChvI regulation. In return, these new findings directed us to uncover better conditions for cultivation of the loss-of-function chvI mutants. Further analyses with reporter gene fusion assays confirmed the direct role of ChvI as a repressor for the rhizobactin and SMc00261 operons. It also confirmed the previously discovered direct activation of the msbA2 operon by ChvI. Methods developed here to identify ChvI targets have proved to be efficient and could be applied to other response regulators. Results Application of electrophoretic mobility shift assay to the identification of ChvI-regulated genes To better understand the role of ChvI as a response regulator, it is necessary to identify genes whose transcription is directly influenced by ChvI.

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