1. By using ultrasonic treatment in media of high ionic strength, the RNA polymerase activities associated with prostatic nuclei and nucleoli can be completely solubilized. Such enzyme preparations are entirely dependent on the provision of added DNA for full activity. 2. The solubilized enzymes from the nucleolar and extranucleolar regions can be separated by ion-exchange chromatography. 3. Based on differences in the optimum DNA templates, pH optima and the effects of ammonium sulphate on the activities in vitro, Mn2+- and Mg2+-specific enzymes are associated with both the nucleolar and extranucleolar regions of prostatic nuclei. 4. Androgenic hormones administered in vivo have a particularly pronounced effect on the activity of Mg2+-dependent enzyme associated with the isolated prostatic nucleolus. 5. Time-course experiments in vivo show that androgens induce a rapid stimulation of the solubilized Mg2+-dependent nucleolar enzyme before a pronounced activation of nucleolar chromatin can be measured. 6. The implications of these findings to the mechanism of action of androgenic steroids are discussed.

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