Molecular Pharmacology, Vol 2, 406-410, Copyright © 1966 by the American Society for Pharmacology and Experimental Therapeutics

Ribonucleic Acid Polymerase Activity in Liver Nuclei from Rats Pretreated with 3-Methylcholanthrene

¹ Department of Pharmacology, Baylor University College of Medicine, Houston, Texas 77025

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.

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ACKNOWLEDGMENT These studies were supported by a grant from the American Cancer Society (E 373).