The differential effects of ions on RNA synthesis in nuclei and nucleoli isolated from neonatal and adult mouse brain

Abstract

The differential effects of ionic conditions on RNA synthesis by nuclei and nucleoli isolated from neonatal and adult mouse brain was studied. Three approaches were used to discriminate between nucleoplasmic and nucleolar RNA synthesis: (1) response of RNA polymerase activity in isolated nuclei and nucleoli to various ionic conditions; (2) sensitivity of incorporation to α-amanitin, a selective inhibitor of nucleoplasmic polymerase II; and (3) use of isolated nucleoli to specifically examine nucleolar polymerase activity. The results of this investigation demonstrated that brain nuclear and nucleolar RNA synthesis respond quite differently to changes in the ionic environment. More specifically, nuclear RNA synthesis appeared to work equally well in the presence of Mg 2+ or Mn 2+ and underwent a two-fold stimulation in activity in response to high salt conditions. In contrast, nucleolar RNA synthesis clearly required the presence of Mg 2+ for significant incorporation and activity was greatly reduced in the presence of high ionic strength. The sensitivity of nuclear RNA synthesis to α-amanitin, while nucleolar activity remained refractory to the drug, suggested that the quantitative differences in polymerase activity under low and high salt conditions were also a reflection of qualitative changes in polymerase activity. Finally, nuclei and nucleoli isolated from neonatal brain tissue were found to respond in a quantitatively and qualitatively similar fashion to changes in their ionic environment as preparations from adult mice.