ABSTRACT
The dmp operon of the pVI150 catabolic plasmid of Pseudomonas sp. strain CF600 encodes the enzymes involved in the catabolism of phenol and methylphenols. The regulator of this dmp pathway, DmpR, is a member of the NtrC family of transcriptional activators and controls transcription of the dmp operon in response to aromatic effector compounds (V. Shingler, M. Bartilson, and T. Moore, J. Bacteriol. 175:1596-1604, 1993). Using a lux gene fusion reporter system, in which the DmpR-regulated operon promoter controls the expression of luciferase activity, we have shown in the study reported here that DmpR is activated by, but responds differentially to, the presence of a wide range of aromatic compounds. In many microbial regulatory systems, including some members of the NtrC family, the response to environmental fluctuations involves information transfer from surface sensory proteins to transcriptional regulators. However, DmpR-mediated activation of phenol metabolism in response to aromatic compounds occurs in the absence of a specific sensory protein. We used hybrids between DmpR and XylR, a structurally related regulator of toluene and xylene metabolism, to demonstrate that it is the amino-terminal domains of these regulators that determine the specificity of transcriptional activation. The results suggest that it is the direct interaction of aromatic compounds with the DmpR and XylR proteins that regulates their transcriptional promoting activity.
