Transcriptional and translational control through the 5'-leader region of the dmpR master regulatory gene of phenol metabolism.

Expression of pathways for dissimilation of toxic aromatic compounds such as (methyl)phenols interfaces both stress-response and carbon catabolite repression control cascades. In Pseudomonas putida, carbon catabolite repression is mediated by the protein Crc - a translational repressor that counteracts utilization of less-preferred carbon sources as growth substrates until they are needed. In this work we dissect the regulatory role of the 5'-leader region (5'-LR) of the dmpR gene that encodes the master regulator of (methyl)phenol catabolism. Using deletion and substitution mutants combined with artificial manipulations of Crc availability in P. putida, we present evidence that a DNA motif within the 5'-leader region is critical for inhibition of the output from the Pr promoter that drives transcription of dmpR, while the RNA chaperone Hfq facilitates Crc-mediated translation repression through the 5'-leader region of the dmpR mRNA. The results are discussed in the light of a model in which Hfq assists Crc to target a sequence within a loop formed by secondary structure of the 5'-LR mRNA. Our results support the idea that Crc functions as a global translational inhibitor to co-ordinate hierarchical carbon utilization in Pseudomonads.