FIG. 4.
Effect of point substitutions within the hctB promoter on in vitro transcription by E. coli σ28 RNA polymerase. All three possible point substitutions were tested at each position from −37 to −24 (A) and from −17 to −4 (B). The wild-type sequence of each predicted promoter element is shown below the respective graph. Changes in promoter activity are shown as the decrease (n-fold) relative to wild-type promoter activity. Decreases greater than 200-fold are not shown as extending below the bottom axis. Each bar represents the mean of three independent experiments.