Figure 7. Shortening and lengthening the spacer between the −35 and −10 elements affect gumB promoter activity.

(A) In vitro transcription assay. 1.15 nM DNA of 544–549 bp fragments of wild-type gumB promoter with a 16-bp-spacer or mutant gumB promoters with a 14-, 15-, 17-, 18- or 19-bp-spacer was incubated with 0.05 U of RNAP and 15 nM His₆-HpaR1 protein if necessary. (B) GUS activity of gumB promoter-gusA reporters in the wild-type strain 8004 and the hpaR1 mutant strain 2736nk. GUS activity was measured after the bacterial cells were cultured in NY medium containing 2% glucose for 24 h. Values given are the means ± standard deviations of triplicate measurements from a representative experiment; similar results were obtained in two other independent experiments.