title: Transcriptional and post-transcriptional control of rRNA synthesis in human liver cells cultured in presence of L-triiodothyronine.
abstract: The synthesis of rRNA in cultured human liver cells grown in the presence of L-triiodothyronine (1.6 x 10(-5)M) was measured by means of polyacrylamide gel electrophoresis using a double labelling technique. The rate of accumulation of rRNA in the cytoplasm as well as the turnover of rRNA in ribosomes remained unchanged in comparison to control cells regardless of growth stage or cell population density. L-triiodothyronine, however, induced an increased synthesis of rpreRNA when added in the early growth phase of sparse cultures. This induction was time dependent and occurred temporarily, but it was never followed by a similar accumulation of mature rRNA. Therefore, in this system two control mechanisms counteracting each other were effective: the increased rpreRNA synthesis indicates a transcriptional control, and the wastage of odd rpreRNA, however, a post-transcriptional control.
mesh_terms: D002478:Cells, Cultured / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008099:Liver; D009694:Nucleic Acid Precursors / Q000096:biosynthesis; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D012270:Ribosomes / Q000378:metabolism; D014158:Transcription, Genetic; D014284:Triiodothyronine / Q000494:pharmacology*
chemical_list: D009694:Nucleic Acid Precursors; D012335:RNA, Ribosomal; D014284:Triiodothyronine