Thyroxine-mediated Control of Ribonucleic Acid Polymerase Activity in Liver of Rana catesbeiana
Michael D. Griswold 1 and Philip P. Cohen 1
From the
1 From the Department of Physiological Chemistry, University of Wisconsin, Madison, Wisconsin 53706
DNA-dependent RNA polymerases from Rana catesbeiana livers were solubilized and chromatographed on DEAE-Sephadex. RNA polymerases I and II were separated and their reaction characteristics determined. The tadpole RNA polymerases exhibited an optimal Mn++:Mg++ activity ratio, a denatured-native template preference and partial subunit structure, similar to those of rat liver RNA polymerases.
The increased activity of RNA polymerases in nuclei after thyroxine treatment of the tadpoles was apparent even after the enzymes were solubilized, chromatographed, and assayed on exogenous templates. Cycloheximide treatment of tadpoles injected with thyroxine had no effect on the increase in RNA polymerase activity. These results suggest that neither changes in endogenous template activity nor de novo synthesis of protein are involved in the increase of RNA polymerase activity.
The Km for UTP of RNA polymerase II from thyroxine-treated tadpoles was found to be approximately one-half that obtained from control RNA polymerases.
These findings are of significance in relation to the intracellular transport of thyroxine to the nucleus and the resulting molecular changes involved in differentiation during metamorphosis.
Submitted on September 28, 1972
Revised on January 19, 1973
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