FIG. 2.

ExsA-dependent transcription requires several amino acids in region 4.2 of E. coli σ⁷⁰. (A) ExsA immunoblots demonstrating that steady-state expression levels are similar in each of the strains used below. (B and C) E. coli strain GA2071 (tightly suppressed for native σ⁷⁰ expression) carrying the P_exsC-lacZ (B) or P_exsD-lacZ (C) transcriptional reporter and the p2UY21 ExsA expression plasmid was transformed with a wild-type σ⁷⁰ expression plasmid or an σ⁷⁰ expression plasmid carrying the indicated mutations in region 4.2. The resulting strains were grown in LB to an OD₆₀₀ of 0.6 and assayed for β-galactosidase activity. The reported values (percentage of activity in the presence of wild-type σ⁷⁰ subunit) are the averages from three independent experiments, and error bars represent the standard errors of the means.