FIG 3.

Assessment of RtcR and RecA dependence of RNA repair operon expression induced by MMC, peroxide stress, and nitrogen limitation. (A) Transcript levels of rtcA and the reference gene rpoD were assessed by qRT-PCR for mid-log-phase cultures of S. Typhimurium 14028s WT, ΔrtcR, and ΔrecA::kan strains in MOPS medium, untreated and treated for 90 min with 3 μM MMC; rtcA transcript levels were normalized to rpoD transcript levels (relative rtcA expression). (B) Transcript levels of rtcB and the reference gene kdgR were assessed by qRT-PCR for mid-log-phase cultures of S. Typhimurium 14028s WT, ΔrtcR, and ΔrecA::kan strains in LB, untreated and treated for 20 min with 1 mM H₂O₂; rtcB transcript levels were normalized to kdgR transcript levels (relative rtcB expression). (C) Cultures of S. Typhimurium 14028s WT, ΔrtcR, and ΔntrC strains were grown to mid-log phase in MOPS medium with ammonium chloride as the nitrogen source; cultures were then split, and cells were washed and resuspended in MOPS medium with either 14.3 mM ammonium chloride (−Arg) or 2.5 mM arginine (+Arg) as the nitrogen source. After 90 min of treatment, total RNA was harvested, and transcript levels of rtcA were assessed by qRT-PCR and normalized to rpoD transcript levels (relative rtcA expression). For all panels, significant differences in relative rtcA or rtcB expression between treated and untreated samples and/or between strains are indicated (*, P < 0.02; **, P < 0.003). Data shown are for three biological replicates for each strain; error bars represent ±1 standard deviation.