FIG. 4.

Northern blotting performed to determine the relative rates of degradation of transcripts produced from the clp locus. The decay was measured in the exponential phase (A) at an OD₆₀₀ of 0.7, with a heat stress at 42°C during 30 min (B) at an OD₆₀₀ of 0.7, and in the stationary phase (C) at an OD₆₀₀ of 1.8. The RNAs were prepared after 0, 3, 4.5, or 6.5 min after rifampin addition (250 μg ml⁻¹). Northern blot analyses of RNAs were performed with a mixture of the three clpP, clpL, and intergenic region-specific probes. In all cases, 15 μg of RNA was applied per lane. This experiment was carried out two times. (D) Semilogarithmic plot of (i) clpP mRNA decay at OD₆₀₀ of 0.7 (solid squares) or after heat-shock (open squares), (ii) clpL mRNA decay at an OD₆₀₀ of 0.7 (solid circles) or after heat shock (open circles), and (iii) cotranscript mRNA decay at an OD₆₀₀ of 0.7 after heat shock (open diamonds). The correlation coefficients (R²) and half-life (T_1/2) were determined for each regression analysis.