FIG. 3.

Effect of single amino acid mutation on σ³²-dependent reporter gene expression. For each mutant, β-galactosidase activity was normalized to the total detectable amount of mutant σ³² protein in cell lysates relative to the amount of wt σ³², as described in Results. Then, all activities were normalized to that observed in wt cell extracts. All values are averages of five to six independent experiments, with the error bars representing the standard deviations. The functional regions of σ³² protein as deduced from the sequence are indicated. Substitutions that reduce interaction with RNAP core enzyme to less than 50% of wt σ³² (Fig. 4 and Table 1) are indicated by asterisks (see text).