Fig 3.

Effects of double point mutations of heptad repeats on ctxAB transcription. β-Galactosidase results from ctxAB::lacZ double point mutations are shown. Results from the WT full-length promoter strain are shown at the far left. The truncated promoter extending only to position −76 is marked as pJW211. The double point mutations are indicated in italics within the sequence. Heptad repeats are numbered and shown as dotted arrows; imperfect repeat 7 is indicated by a dashed arrow. The black bars indicate O395 WT toxT strains, and the gray bars indicate O395 ΔtoxT strains. The fold difference in β-galactosidase activities between the WT and ΔtoxT strains is labeled above each promoter. The asterisks indicate statistically significant fold differences in β-galactosidase results between O395 WT toxT PctxAB and O395 ΔtoxT PctxAB strains according to Student's t test (P < 0.03). Each experiment was repeated a minimum of three times, and the data shown are mean values, with the standard deviations indicated by error bars.