Nucleolar RNA synthesis in the liver of partially hepatectomized and cortisol-treated rats.

RNA synthesis by isolated nucleoli from rat liver is significantly enhanced 12--14 h after partial hepatectomy and 4 h after cortisol administration. The increased RNA synthetic capactiy is demonstrable also in the respective high salt nucleolar extracts and in Biogel A-1.5 filtration fractions of the nucleolar extracts. DNA saturation experiments using nucleoli and Biogel fractions from control and treated animals as RNA polymerase source, have demonstrated, that independent of the extent of RNA synthesis, saturation of transcription is reached at the same concentration of exogenous template. We conclude that the activity and not the amount of nucleolar RNA polymerase is increased as a result of partial hepatectomy or cortisol administration. Parallel to the effects on RNA polymerase, the activity, of RNA-degrading enzymes present in nucleoli is also enhanced by the same treatment.