Activation of the xylDLEGF promoter of the TOL toluene-xylene degradation pathway by overproduction of the xylS regulatory gene product.

The xylS regulatory gene of the Pseudomonas putida TOL plasmid (pWWO) has been cloned under the transcriptional control of the Escherichia coli tac promoter in a broad-host-range controlled-expression vector. Induction with isopropylthiogalactoside allowed overproduction and characterization of the xylS product by specific interaction with the TOL meta-cleavage pathway operator-promoter region (OP2) in vivo in E. coli. Examination of plasmid-specified polypeptides in E. coli maxicells led to identification of the xylS product as a 36-kilodalton polypeptide. The operator sequences required for xylS interactions lay upstream of the OP2 transcriptional start, and the xylS gene product recognized this region even in the absence of known coinducers.