Figure 4. Effect of amino acid substitutions in Region 2.4 of σ²⁸ on mutations at −10 promoter region.

D81A σ²⁸28 and R84A σ²⁸ uniquely suppress single nucleotide changes at positions −11G and −12C of the tar promoter respectively (A and B), whereas R74A σ²⁸ shows less relative activity than wt σ²⁸ on mutant promoters with single nucleotide changes at positions −10 to −14 of the tar promoter (C). For panels A and C, β-galactosidase activity driven by each σ²⁸ variant on mutant tar promoters is shown as a percentage of the β-galactosidase activities of the same σ²⁸ variant on the wt promoter. For panel B, absolute β-galactosidase activity (Miller Units) driven by D81A σ²⁸ and R84A σ²⁸ on mutant tar promoters is indicated. Activities of less than 0.5 Miller Units is at the background level of this assay. Assay strains are as described in Fig 1B. Below the x-axis, mutation and position indicate the base change at the different promoter positions; σ²⁸ indicates the wild type or substituted derivative. All values are averages of three to four independent experiments; error bars indicate 1 standard deviation.