Estrogen regulates the number of RNA polymerase II molecules in rooster liver

Administration of estrogen to roosters causes an increase in the activities of DNA-dependent RNA polymerases I and II in nuclei isolated from liver. In an effort to determine the cause of this increased transcriptional activity, we have examined the activity of RNA polymerase II that we have solubilized from nuclei of normal, estrogen-stimulated, and estrogen-withdrawn roosters. In addition, we have measured the actual numbers of RNA polymerase II molecules per nuclear equivalent of DNA in livers of roosters in each estrogenic state by the technique of [3H]amanitin-binding. The administration of estrogen is attended by a 2-fold increase in enzymatic activity of solubilized RNA polymerase II per liver nucleus within 24 h. In addition, there is a 2-fold increase in the number of RNA polymerase II molecules per nucleus in the livers of these animals after the administration of estrogen. During withdrawal from estrogen for 14 days, the activities of RNA polymerases I and II in isolated nuclei and the activity of solubilized RNA polymerase II return to the unstimulated levels. Moreover, the [3H]amanitin-binding capacity of nuclear extracts from the livers of roosters in various stages of hormonal stimulation closely mimics the RNA polymerase II activity of the same extracts. These observations indicate that estrogen exerts a rigid control over the population of RNA polymerase II molecules in avian liver.