Altering the promoter region of qstR affects natural transformation. Variants lacking either the HapR-binding site or the putative CRP-S site or containing site-directly changed CRP-S motifs were tested for natural transformability, relative expression of the selected genes, ComEA protein production, and DNA uptake (panels A-D) as described for the previous figures. The tested strains are indicated in the legend, and all experiments were performed at least three independent times. Error bars represent the standard deviation. Statistically significant differences with respect to natural transformation were determined by Student’s t- tests. **P < 0.01, ***P < 0.001, n.s. = not significant. The value of the detection limit was used for the statistics of non-transformable strains.