Induction of the expression of ohr and ohrR by peroxides. Cells were grown in LB medium to an OD570 nm of 0.4. ohr::lacZ (β-galactosidase) and ohrR::uidA (β-glucuronidase) expression was analysed 2 and 3 h after OHP addition. No addition (closed diamonds), 0.25 mM CuOOH (closed triangles), 1.6 mM tBOOH (open squares), 10 mM H2O2 (open circles). Enzymatic activities are expressed as nmole of substrate hydrolysed per min and per mg of protein. Results are the average of four independent experiments; the standard deviation is indicated by bars.