To study the effect of phenobarbital on transcription of hepatic ribosomal precursor RNA (45 S RNA), three experiments were performed in adult male rats receiving single daily intraperitoneal injections of 0.9% NaCl or phenobarbital (100 mg/kg) for 1 or 4 days: measurement of the labeling of hepatic nuclear RNA with L-[methyl-3H]methionine, determination of nucleolar RNA polymerase activity, and measurement of alkaline nuclear ribonuclease activity. Labeling of nuclear RNA with [methyl-3H]methionine increased approximately 100% and 50% in rats treated for 1 and 4 days, respectively, with phenobarbital. Phenobarbital for 1 or 4 days did not affect nucleolar RNA polymerase activity measured in the presence of high ionic media and α-amanitin. With nonlabeled ribosomal RNA or 45 S [3H]RNA as substrate, nuclear alkalne ribonuclease activity in phenobarbital-treated rats was unaltered. These data confirm our previous finding that phenobarbital-induced stabilizations of 45 S RNA molecules accounts for the approximately 2-fold increase in cellular concentration of 45 S RNA in rats treated for 4 days with phenobarbital. A single dose of phenobarbital may stimulate methylation of newly formed 45 S RNA molecules normally degraded in the nucleus, thereby increasing transport of ribsomal subunits to the cytoplams.
- Copyright ©, 1974, by Academic Press, Inc.