Transcription in aging: the response of rat liver nuclear RNA polymerases to cycloheximide in vivo.

Experiments were performed to address the known relationship between diet and longevity. The acute response of rat liver nuclear RNA polymerases to inhibition of protein synthesis by cycloheximide (10 mg/kg) was quantitated in rats of varying ages. Thirty minutes after cycloheximide administration, there was a "compensatory" 1.5--2-fold increase in RNA polymerase II activity at all ages. Nucleolar RNA polymerase I activity was significantly diminished only up to 4 months, indicating a loss in tight control coupling of protein synthesis to rRNA synthesis with age.