Protein binding in vivo to OP2 promoter of the Pseudomonas putida TOL plasmid.

The transcription of OP2 encoding enzymes for m-toluate catabolism on the Pseudomonas putida TOL plasmid is activated by basal-level XylS protein in the presence of m-toluate or by overproduced XylS protein in the absence of m-toluate. In this study, in vivo dimethyl sulfate (DMS) footprinting was performed to understand the mechanism of transcriptional regulation of OP2 promoter by XylS. In the presence of overproduced XylS without m-toluate, several protected nucleotides were observed, indicating the binding of RNA polymerase to DNA. However, the protection was canceled upon addition of m-toluate. These results suggest that RNA polymerase is retained by XylS on the OP2 promoter in the absence of inducer, and is released by m-toluate binding to XylS, concomitant with transcription.