FIGURE 1.

H₂O₂ induces stringent regulation. A and B, transcription of the stringently controlled ribosomal protein genes rpsM (A) and rplN (B) was evaluated using quantitative real time and reverse transcription PCR, respectively, in wild-type (WT) and dksA mutant bacteria. Transcript levels were normalized to the housekeeping σ factor rpoD. Bacterial cultures grown overnight in LB medium were subcultured 1:10 for 30 min in PBS with or without 1 mm H₂O₂. The data in A represent the mean ± S.E. (error bars) from three independent experiments. **, p < 0.01. C, DksA protein levels were estimated at various times after the bacteria were challenged with 1 mm H₂O₂ in PBS. D, bacterial growth in LB medium is shown.