FIG. 4.

Stabilities of des and bulk mRNA. The des mRNA levels at 37°C (open triangles) or 20°C (filled triangles) were determined by quantifying the radioactivity of the bands of the Northern blot shown in Fig. 3 and from dot blots of RNA hybridized with a radiolabeled probe specific for des, as described in Materials and Methods. The samples for dot blot analysis were taken at the same times as those for the Northern analysis, as indicated in the legend of Fig. 3. Each value is the average of the results of two independent experiments. The bulk RNA decay was measured as described in Materials and Methods. Samples at 37°C (open circles) were taken at 0, 1, 3, 6, 12, and 24 min after inhibition of RNA synthesis. Samples at 20°C (filled circles) were taken at 0, 6, 12, 24, 48, and 70 min after inhibition of RNA synthesis.