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J. Bacteriol., 03 1995, 1485-1490, Vol 177, No. 6
LC Ng, CL Poh and V Shingler
Pseudomonas putida P35X (NCIB 9869) metabolizes phenol and
monomethylphenols via a chromosomally encoded meta-cleavage pathway. We
have recently described a 13.4-kb fragment of the chromosome that codes for
the first eight genes of the catabolic pathway and a divergently
transcribed positive regulator, phhR. The eight structural genes lie in an
operon, the phh operon, downstream of a -24 TGGC, -12 TTGC promoter
sequence. Promoters of this class are recognized by RNA polymerase that
utilizes the alternative sigma 54 factor encoded by rpoN (ntrA) and are
positively regulated by activators of the NtrC family. In this study, we
have identified the coding region for the 63-kDa PhhR gene product by
nucleotide sequencing of a 2,040-bp region and polypeptide analysis. PhhR
was found to have homology with the NtrC family of transcriptional
activators, in particular with DmpR, the pVI150-encoded regulator of
(methyl)phenol catabolism by Pseudomonas sp. strain CF600. By using a
luciferase reporter system, PhhR alone was shown to be sufficient to
activate transcription from the phh operon promoter in an RpoN+ background
but not an RpoN- background. Luciferase reporter systems were also used to
directly compare the aromatic effector profiles of PhhR and DmpR. Evidence
that the difference in the growth substrate ranges of strains P35X and
CF600 is due to the effector activation specificities of the regulators of
these systems rather than the substrate specificities of the catabolic
enzymes is presented.
Copyright © 1995, American Society for Microbiology
Aromatic effector activation of the NtrC-like transcriptional regulator PhhR limits the catabolic potential of the (methyl)phenol degradative pathway it controls
Institute of Cell and Molecular Biology, Umea University, Sweden.
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