Promoter-upstream activator sequences are required for expression of the xylS gene and upper-pathway operon on the Pseudomonas TOL plasmid



Stimulation of transcription from the Pseudomonas TOL plasmid xylS gene promoter (Ps) and the upperpathway operon promoter (Pu) is dependent on the positive regulator protein XylR activated by an effector molecule such as 3-cholorotoluene, and on RpoN, an RNA polymerase sigma factor. Mutational analysis of the Ps and Pu promoters showed that upstream activator sequences located between -110 and -218bp upstream of the main transcription initiation point are required for regulated expression from these promoters. A search for homologous nucleotide sequences in the -110to -218bp region in Pu and Ps revealed conserved sequences that may act as putative recognition sequences for the XylR protein. Ps and Pu exhibit another well-conserved region at around 50 bp, which is homologous to corresponding sites in other RpoN-dependent promoters and may constitute a binding site for integration host factor (IHF).