Transcriptional activation of the CrcZ and CrcY regulatory RNAs by the CbrB response regulator inPseudomonas putida

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The CbrAB two-component system has been described as a high-ranked element in the regulatory hierarchy ofPseudomonas putidathat controls a variety of metabolic and behavioural traits required for adaptation to changing environmental conditions. We show that the response regulatory protein CbrB, an activator of σN-dependent promoters, directly controls the expression of the small RNAs CrcZ and CrcY inP. putida. These two RNAs sequester the protein Crc, which is a translational repressor of multiple pathways linked to carbon catabolite repression. We characterized thein vivoandin vitroactivation by CbrB at bothcrcZandcrcYpromoters, and identified new DNA sequences where the protein binds. IHF, a co-activator at many σN-dependent promoters, also binds to the promoter regions and contributes to the activation of the sRNAs. CbrB phosphorylation is necessary at physiological activation conditions, but a higher dose of the protein allowsin vitrotranscriptional activation in its non-phosphorylated form. We also show there is some production of CrcY coming from an upstream promoter independent of CbrB. Thus, CbrAB constitute a global signal transduction pathway integrated in a higher regulatory network that also controls catabolite repression through the expression of the two regulatory RNAs CrcZ and CrcY.

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