FIG 4.

Comparison of RtcR and RecA dependence of RNA repair operon expression induced by MMC and cisplatin. Cultures of S. Typhimurium 14028s WT, ΔrtcR, and ΔrecA::kan reporter strains, which have xylE replacing the first gene of the RNA repair operon, were grown to mid-log phase in LB medium and split into portions that were untreated or treated with 3 μM MMC for 90 min or 110 μM cisplatin for 180 min. After treatment, the cells were harvested and assayed for XylE (catechol dioxygenase) activity over a period of time, as described in Materials and Methods. The activity is expressed in nanomoles of catechol oxidized per minute per 10⁸ cells. Significant differences in XylE activity between treated and untreated samples are indicated (*, P < 0.004). Data shown are the average from at least three biological replicates for each strain; error bars represent ±1 standard deviation.