Initiation of transcription at the bacterial glnAp2 promoter by purified E. coli components is facilitated by enhancers

The initiation of transcription from the nitrogen-regulated promoter glnAp2 requires RNA polymerase containing σ 54, the transcriptional activator NR I, and the protein kinase NR II, responsible for the conversion of NR I to the active NR I-phosphate. NR I-phosphate does not increase the ability of σ 54-containing RNA polymerase to bind to the promoter, but rather stimulates the conversion of an initial promoter:polymerase complex to the transcriptionally active open complex. The presence on the DNA template of high-affinity binding sites for NR I/R I-phosphate, normally located 130 and 100 bp upstream of the site of transcription initiation, results in a 4- to 5-fold lowering of the concentration of NR I required for the formation of the open complex. These high-affinity NR I binding sites facilitate open complex formation when they are moved to positions 700 bp further upstream or 950 bp downstream of glnAp2 on linear DNA templates.