Regulatory activity of MvaT-like proteins in Pseudomonas putida

The genome of Pseudomonas putida strain KT2440 contains five paralogous proteins belonging to the H-NS-like MvaT group of transcription regulators. We analyzed the global effects of eliminating two of these proteins, TurA and TurB, on the P. putida KT2440 transcriptome. Our results indicated that TurA acts prevalently as repressor of many genes belonging to a broad range of functional classes in both mid-exponential and early stationary phases. Likewise, TurB acts in both these growth stages on genes of many functional classes. However, the size of TurB regulon appears to be five-fold smaller than in the case of TurA. Furthermore, TurB does not act prevalently as repressor. The degree of overlap between the TurA and TurB regulons is limited. In a case where regulon interception occurs, i.e. a cluster of genes related to those for biosynthesis of lipodepsinonapeptide phytotoxins, we show that TurA and TurB can act in concert. In addition, our results strongly indicate that the expression of TurB, along with that of other two paralogs, TurD and TurE, is submitted to TurA. In a second part of this work, we addressed by bacterial two-hybrid assays the issue of the degree of dimerization promiscuity among the Tur paralogs. Our results indicate that each Tur paralog can potentially act both as homomer and as heteromer in combination with any other paralog. We speculate that, if the various species of homomers and heteromers recognized certains DNA sites with different affinities, and if the expression of the five paralog genes responded to different environmental signals, this would allow a tremendous chance to fine-tune the expression of the Tur regulons.