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Abstract:
The CbrAB two-component system has been
described as a high-ranked element in the regulatory
hierarchy of Pseudomonas putida that 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
in P. putida. These two RNAs sequester the protein
Crc, which is a translational repressor of multiple
pathways linked to carbon catabolite repression. We
characterized the in vivo and in vitro activation by
CbrB at both crcZ and crcY promoters, 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 allows in vitro transcriptional
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.
