Figure 1.

Effect of translational fidelity on σ^S-dependent gene expression and σ^S levels during growth and glucose starvation. (A) Growth of the wild-type (Wt/Δ14; closed squares) and the rpsL141 mutant (S12/Δ14; open circles) strains under aerobic conditions. The arrows and numbers indicate the time at which samples were taken for catalase activity (B) and superoxide dismutase activity (C). Catalase and superoxide dismutase activities were determined and expressed as described in Materials and Methods. One unit of catalase is defined as the amount of enzyme per milligram of total protein that degrades 1 μmol of hydrogen peroxide in 1 min at 25°C (Dukan et al. 2000). One unit of superoxide dismutase is defined as the amount of enzyme per milligram of total protein that inhibits the rate of cytochrome c reduction by 50% at 25°C. Filled bars represent the wild type and open bars represent the rpsL141 mutant. (D) Growth (open symbols) and katE promoter activity (closed symbols) in the wild type (MBN7; squares) and rpsL141 mutant (MBN8; circles). (E) Levels of σ^S in the wild type (DV206) and rpsL141 mutant (ÅF1), as indicated, during growth and during carbon starvation. The sampling times are indicated in D. (F) Levels of σ^S in the wild type (DV206) and rpsD12 mutant (MBN27) during growth and glucose starvation. Samples were taken in exponential growth (Log), early glucose starvation, depicting the highest σ^S levels reached (SP), and cultures starved overnight (ON). (G) Quantitative representation, using the Image Gauge software, of the data shown in F. (Filled bars) Wild type; (unfilled bars) rpsD12 mutant. All experiments were repeated at least three times. Representative results are shown.