The rapid acceleration of hepatic nuclear ribonucleic acid breakdown by actinomycin but not by ethionine.

The effects of two different inhibitors of rat liver RNA synthesis, actinomycin D and ethionine, upon liver RNA metabolism have been studied and compared. Whereas ethionine administration leads to a relatively slow loss of about 30% of total nuclear RNA over a period of 12 to 16 hours involving the molecular species representative of the total pool, the administration of actinomycin D is followed by a rapid loss of recently labeled moieties of nuclear RNA. The pretreatment of animals with ethionine had no significant effect upon the loss of nuclear RNA induced by actinomycin D. The labeling of cytoplasmic RNA with erotic acid-6J4C was inhibited by each agent. It is considered probable that the different patterns of response of hepatic nuclear RNA to these two agents are a reflection of the different mechanisms whereby they inhibit RNA synthesis. It is concluded that compounds which bind to DNA, such as actinomycin D, have effects on nuclear RNA metabolism in addition to those resulting from the inhibition of RNA synthesis.