Fig. 4.

Effects of Bt₂cAMP with or without hLDL on mRNA stability. Bt₂cAMP-presensitized cells were exposed to Bt₂cAMP (2.5 mM; closed circles) or Bt₂cAMP plus hLDL (100 μg/ml; open circles) for 24 h before the addition of actinomycin D (10 μg/ml; A) or 5,6-dichloro-1-h-d-ribofuranosylbenzimidazole (DRB) (100 μg/ml; B) to inhibit gene transcription. The 24 h time point represents the time of maximal increase in LRP transcript levels in granulosa cells, as shown in Fig. 3. Total RNA was isolated from the cells at the indicated times after the addition of transcription inhibitors and processed for LRP mRNA determination by RPA. The data shown, expressed as percentages of the initial LRP content before inhibitor addition, are from a representative experiment, and the mean mRNA half-lives determined from several such experiments are given in the text. The extent of variation among the data points was between 9.1% and 13.7%.