Effects of glucocorticoid and cycloheximide on the activity and amount of RNA polymerase I in nuclei of rat liver.
The activity of the template-engaged form of RNA polymerase I from livers of adrenalectomized rats was about 50-60% of that of normal control rats, and increased about 2-fold at 6 h after the administration of dexamethasone. However, no change was found in the activity of the 'free' form of RNA polymerase I or the template-engaged form of RNA polymerase II. Immunochemical studies using guinea-pig anti-(RNA polymerase I) serum disclosed that the total number of RNA polymerase I molecules did not vary during the treatment with dexamethasone. Cycloheximide caused a rapid decrease in the template-engaged form of RNA polymerase I activity in normal rats and in dexamethasone-treated (6 h) adrenalectomized rats, to the value in adrenalectomized rats, but affected it only slightly in adrenalectomized rats. The elongation rate of rRNA-precursor synthesis in liver nuclei was not affected by a change in the concentration of circulating dexamethasone. From these results, it is concluded that about half the rRNA-precursor synthesis in rat liver is regulated by glucocorticoids, probably through the synthesis of short-lived protein(s) which may play a role in conversion of the 'dormant' form of RNA polymerase I into the 'engaged' form.
D000315:Adrenalectomy; D000818:Animals; D002467:Cell Nucleus / Q000201:enzymology*; D003513:Cycloheximide / Q000494:pharmacology*; D003907:Dexamethasone / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology*; D008099:Liver / Q000201:enzymology* / Q000648:ultrastructure; D008297:Male; D009694:Nucleic Acid Precursors / Q000378:metabolism; D012318:RNA Polymerase I / Q000276:immunology / Q000378:metabolism*; D012322:RNA Precursors; D012335:RNA, Ribosomal / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
D005938:Glucocorticoids; D009694:Nucleic Acid Precursors; D012322:RNA Precursors; D012335:RNA, Ribosomal; D003907:Dexamethasone; D003513:Cycloheximide; D012318:RNA Polymerase I