title: Chromatin-bound and free RNA polymerase A activities in rat thymus cells following glucocorticoid treatment.
abstract: Treatment of rat thymus cell suspensions with dexamethasone resulted in inhibition of engaged RNA polymerase A, without significant change in free pool activity. Studies with the re-initiation inhibitor, rifamycin AF/0-13, and measurements of numbers of RNA polymerase A molecules and of elongation rates showed that the inhibition of pre-rRNA synthesis resulted from a decrease in elongation rate. This effect was selectively abolished by mild proteolysis of nuclei. It is concluded that glucocorticoid treatment of rat thymus cells suppresses 45 S rRNA synthesis primarily by decreasing the polyribonucleotide elongation rate, rather than by effecting a change in enzyme redistribution or concentration.
mesh_terms: D000818:Animals; D002843:Chromatin / Q000201:enzymology*; D003907:Dexamethasone / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D012318:RNA Polymerase I / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000096:biosynthesis; D051381:Rats; D012294:Rifamycins / Q000494:pharmacology; D013950:Thymus Gland / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D002843:Chromatin; D012335:RNA, Ribosomal; D012294:Rifamycins; D003907:Dexamethasone; D012318:RNA Polymerase I