RT Journal Article SR Electronic T1 Ribonucleic Acid Polymerase Activity in Liver Nuclei from Rats Pretreated with 3-Methylcholanthrene JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 406 OP 410 VO 2 IS 5 A1 EDWARD BRESNICK YR 1966 UL http://molpharm.aspetjournals.org/content/2/5/406.abstract AB The intraperitoneal administration of 3-methylcholanthrene is attended by an increase in RNA polymerase activity in the liver nuclei. The maximal increase is reached between 6 and 12 hr after administration of the agent; enzyme activity returns to control values by 48 hr. The administration of actinomycin D or cycloheximide prevents the rise in nuclear RNA polymerase activity. No increase is apparent when the enzyme is assayed at high salt concentrations, i.e., 0.7 M ammonium sulfate. These data suggest that 3-methylcholanthrene may cause the synthesis of or activate a "derepressor" substance that allows for an increased template activity of the liver chromatin in transcription. ACKNOWLEDGMENT These studies were supported by a grant from the American Cancer Society (E 373).