RNA metabolism in primary cultures of Xenopus laevis kidney cells: III. Processing of rRNA precursor in growing and resting cells

Abstract The rate of processing of ribosomal RNA (rRNA) precursor was measured in primary cultures of Xenopus laevis kidney cells in growing and resting states. The kinetic studies on labeling of the precursor RNA and 18 and 28S rRNA in cumulative and pulse-chase experiments revealed that the precursor accumulated and reached a steady state much more rapidly and 18 and 28S rRNA started to appear more rapidly in actively growing cells. Furthermore, the halflives of the precursor RNA were estimated to be 10 and 30 min for growing and resting cells, respectively. These results clearly support the view that not only the transcription and breakdown which have already been shown to be important steps for regulation, but the processing of the precursor RNA molecule would also be controlled upon alteration of the cellular growth rate.