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 pro moter of the TOL (toluene biodegradation) plasmid pWW0 of Pseudomonas putida is activated at a distance by the XylR protein, of the NtrC fam ily of transcriptional regulators. Since contacts between XylR bound t o upstream activating sites and the RNA polymerase require the looping out of the intervening DNA segment, the intrinsic curvature, the bend ability of the corresponding sequence, and the spatial effects of prot ein-induced DNA bending have an influence on promoter activity. Unlike other sigma(54)-dependent promoters, Ps does not require the structur al 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, inst ead, that the looping out of intervening DNA sequences in Ps would res ult from the exacerbation of a preexisting static bend within the regi on, assisted by the histone-like protein HU.