AROMATIC EFFECTOR ACTIVATION OF THE NTRC-LIKE TRANSCRIPTIONAL REGULATOR PHHR LIMITS THE CATABOLIC POTENTIAL OF THE (METHYL)PHENOL DEGRADATIVE PATHWAY IT CONTROLS

Pseudomonas putida P35X (NCIB 9869) metabolizes phenol and monomethylp henols via a chromosomally encoded meta-cleavage pathway. We have rece ntly described a 13.4-kb fragment of the chromosome that codes for the first eight genes of the catabolic pathway and a divergently transcri bed positive regulator, phhR, The eight structural genes lie in an ope ron, the phh operon, downstream of a -24 TGGC, -12 TTGC promoter seque nce. Promoters of this class are recognized by RNA polymerase that uti lizes 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 transcriptio nal 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 t o activate transcription from the phh operon promoter in an RpoN(+) ba ckground but not an RpoN(-) background. Luciferase reporter systems we re also used to directly compare the aromatic effector profiles of Phh R and DmpR. Evidence that the difference in the growth substrate range s of strains P35X and CF600 is due to the effector activation specific ities of the regulators of these systems rather than the substrate spe cificities of the catabolic enzymes is presented.