Response of Rat Thymic Nuclear RNA Polymerase to Cortisol Injection

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Abstract
Properties of the RNA polymerase of rat thymic nuclei have been examined with the view of assessing alterations in activity of this enzyme in response to cortisol injection. The polymerase resembled closely that described for other mammalian tissues. The presence of all 4 nucleoside triphosphates was necessary for maximal enzymatic activity. The polymerase was inhibited by actinomycin D or RNase. Injection of cortisol (5 mg/ 100 g body weight) into rats 3 hr. prior to sacrifice resulted in a significant lowering of the rate of incorporation of triphosphates into nuclear RNA. Thymic nuclei also incorporated nucleoside mono- and diphosphates but not uridine into RNA; cortisol injection inhibited the rate of incorporation of these nucleoside phosphates. RNA polymerase activity was also decreased in aggregate enzyme preparations obtained from nuclei of thymic tissue from cortisol injected rats. The effect of the steroid appears to be independent of intranuclear pool sizes of RNA precursors or of nuclear transport factors.