FIG. 1.

Organization of the tcpA and ctx promoters. Base pair sequences of the ctx (A) and tcpA (B) promoter fragments relative to their transcriptional start sites (+1) are shown. The core promoter −10 and −35 elements are underlined. The promoter regions protected by ToxT from DNase I (72) are denoted by solid gray bars above the sequence. At ctx, the low-affinity (L; light gray) and high-affinity (H; dark gray) ToxT binding sites are shown. The low-affinity sites are those that require higher concentrations of ToxT to show protection (72). Proposed ToxT consensus sites, toxboxes, are indicated by arrows, and the consensus toxbox sequence is shown in panel C, where r = A/G, w = A/T, and y = C/T. (C) The IHF consensus site centered at −162 of tcpA is indicated by a black bar. Putative H-NS nucleation sites with seven or more matches to the 10-bp H-NS consensus (35) are indicated in boldface letters.