Alteration of Deoxyribonucleic Acid-dependent Ribonucleic Acid Polymerase Activities in Amphibian Liver Nuclei during Thyroxine-induced Metamorphosis

Abstract

Abstract DNA-dependent RNA polymerase activity was determined in isolated tadpole liver nuclei. RNA polymerase I and II activities could be differentiated in situ by the use of α-amanitin. The nuclear RNA polymerases were shown to respond to Mn2+ and Mg2+ in a manner similar to that reported for the same enzymes from other eukaryotes and revealed a biphasic activity curve in the presence of increased ammonium sulfate concentration. It was shown that the two peaks of activity were the result of different optimal activities in the presence of ammonium sulfate of RNA polymerase I (50 mm) and of RNA polymerase II (300 mm). The nearest neighbor and base composition analyses revealed a marked change in the ratio of AMP + UMP: GMP + CMP when the isolated nuclei were assayed in the presence of α-amanitin. While the rate of RNA synthesis with isolated nuclei was nonlinear, this appeared not to be the result of RNA polymerase inactivation or of degradation of the product by ribonuclease. Thyroxine administration, either by injection or immersion of tadpoles, caused marked stimulation of both RNA polymerases I and II. The increases in activities of both enzymes were not detectable until at least 4 days after tadpole immersion in 2.0 x 10-8m thyroxine. An increase in mitochondrial carbamyl phosphate synthetase paralleled that of the RNA polymerases. There was no significant time lag between the increase in RNA polymerase I, RNA polymerase II, and carbamyl phosphate synthetase activities. The increase in RNA polymerase activities was also observed during natural metamorphosis.