THE SIGMA(54)-DEPENDENT PROMOTER PS OF THE TOL PLASMID OF PSEUDOMONAS-PUTIDA REQUIRES HU FOR TRANSCRIPTIONAL ACTIVATION IN-VIVO BY XYLR

In the presence of toluene and xylenes, the sigma(54)-dependent Ps promoter of the TOL (toluene biodegradation) plasmid pWW0 of Pseudomonas putida is activated at a distance by the XylR protein, of the NtrC family of transcriptional regulators. Since contacts between XylR bound to upstream activating sites and the RNA polymerase require the looping out of the intervening DNA segment, the intrinsic curvature, the bendability of the corresponding sequence, and the spatial effects of protein-induced DNA bending have an influence on promoter activity. Unlike other sigma(54)-dependent promoters, Ps does not require the structural aid of the integration host factor to assemble a specific promoter geometry required for transcriptional initiation. In vivo analysis of transcriptional activity in various genetic backgrounds suggests, instead, that the looping out of intervening DNA sequences in Ps would result from the exacerbation of a preexisting static bend within the region, assisted by the histone-like protein HU.