Fig 1.

Map of the ctxAB promoter region. The black bar over the sequence indicates DNase I footprinting protection by ToxT (45). The ToxT binding sites toxbox 1 and toxbox 2, determined in this study by mutagenesis and copper-1,10-phenanthroline footprinting, are illustrated by arrows. The base pair at position −76 is boxed to indicate the endpoint of the minimal ctxAB construct that is activated by ToxT. Heptad repeats are numbered underneath the sequence and are indicated by dotted arrows; imperfect repeat 7 is indicated by a dashed arrow. The transcriptional start site is indicated by a bent arrow, and the putative −10 and −35 promoter elements are boxed.