FIG. 4.

Expression of the rnr gene under different conditions. Total RNA was obtained from cells grown under the indicated conditions, and the mRNA levels of the rnr gene were compared by real-time RT-PCR. The conditions compared were as follows: (i) 2 hours after a cold shock in LB medium (transfer from 30°C to 10°C) relative to the mRNA levels immediately before the cold shock (0 h); (ii) exponential growth in LB medium at 10°C, 20°C, or 30°C, with the mRNA levels at 30°C taken as a reference; (iii) entry into stationary phase (A₆₀₀, 2.2 [Stat]) versus exponential phase (A₆₀₀, 0.6 [Exp]) in LB medium at 30°C, with the latter taken as a reference; and (iv) exponential growth (A₆₀₀, 0.6) at 30°C in a minimal salts medium containing succinate (M9+Sc) or citrate (M9+Cit) as the carbon source compared to LB medium under the same conditions. The relative amount of mRNA for each gene (experiment versus control) was determined following the 2^−ΔΔCt method (23), using the mRNA levels of rpoN as an internal control in all cases except for the cold-shock assays, where rpoD was used. The error bars indicate standard errors.