An artificial enhancer with multiple response elements stimulates prokaryotic transcriptional activation mediated by various regulatory proteins

Regulation of transcription by the form of RNA polymerase that contains sigma(N) involves activation at a distance by activators bound to sites located far upstream of the transcription start site, which contact RNA polymerase bound to the promoter via formation of a DNA loop. At the g/nAp2 promoter, binding sites for the activator NtrC show features characteristic of eukaryotic enhancers. A multiple response element containing binding sites for five sigma(N)-dependent activators from different systems has been cloned in different positions relative to the glnAp2 promoter. These promoter regions indeed allowed activation in vivo by each regulator, thus showing that transcription from an eubacterial promoter may be controlled in a very versatile way by different signals. The activation capability of each activator has been assessed in relation to its concentration, and the presence and relative positions of the corresponding binding sites in the DNA. Results show that most activators can function from any position. However, activation mediated by DctD-L64 was very sensitive to changes in the position of its binding sites. Transcriptional activation by combinations of two regulators was also tested and no significant synergism or interference was detected. Mapping of the 5' ends of the transcripts showed that neither the activator nor the position from which they activate influences selection of the transcription start site.