[Synthesis and maturation of RNA after proliferative stimulation: comparison between fibroblasts and lymphocytes]

Comparison of the regulation of RNA metabolism following stimulation of mammalian fibroblasts in culture and of lymphocytes reveals that in both systems it is the processing and transport of gene transcripts which are the initial targets of the activation process rather than the gene transcription itself. In the case of the human lymphocyte, the time required for appearance of labeled RNA in cytoplasm after addition of labeled uridine diminishes progressively with duration of incubation with mitogen. Using adenine as a marker diminishes the latent period between addition of label and its appearance in cytoplasmic RNA. This may be due to polyadenylation of preexisting transcripts which are turned over at a high rate in the nucleus of resting cells but stabilized, processed and exported to the cytoplasm after stimulation.