FIG. 1.

Organization of the xylR-xylS intergenic region. The Ps1 promoter includes UASs (large boxes) for the master activator of the system, XylR; the −12/−24 sequences recognized by ς⁵⁴-containing RNA polymerase (small boxes); and two potential IHF binding sites (shaded bars). Also indicated are consensus ς⁷⁰-containing RNA polymerase-binding sites (−10 to −35) and the transcription initiation point (+1) for the xylR gene Pr tandem promoters Pr1 and Pr2 and for the xylS gene Ps2 promoter. The nucleotide sequence of the Pr promoter region that overlaps the Ps1 UASs is shown in detail.