Experimental conditions affecting ribonucleic acid polymerase in isolated rat liver nuclei. Effect of nucleoside triphosphate concentration, temperature, ammonium sulphate and heparin.

1. The conditions affecting the activity of RNA polymerase in isolated rat liver nuclei were studied with Mg(2+) or Mn(2+) as activating ions. 2. The enzyme assayed with Mg(2+) and at low ionic strength is saturated by a lower concentration of nucleotide substrates than if assayed with Mn(2+) at low ionic strength or with either ion at high ionic strength. 3. At low and at high ionic strength the incorporation of AMP is affected in a similar way by variations in the temperature of incubation. Preincubation at 37 degrees impairs the AMP incorporation. 4. Heparin stimulates the RNA polymerase activity in the presence of Mn(2+). 5. Both ammonium sulphate and heparin ;restart' the reaction if added after 15min., the effect being more marked with ammonium sulphate than with heparin, and also more marked in the presence of Mn(2+) than of Mg(2+). 6. alpha-Amanitin abolishes the effect of ammonium sulphate and of heparin.