Correlation in isolated nuclei of template-engaged RNA polymerase II, ovalbumin mRNA synthesis, and estrogen receptor concentrations.

Template-engaged and total RNA polymerase II molecules were quantitated in isolated nuclei at various stages of estrogen withdrawal and secondary stimulation by using [3H]amanitin titration assays. Estrogen receptors, RNA transcriptional activity, and ovalbumin mRNA were also measured, and comparisons were made between these parameters to determine whether any significant correlations exist. In isolated nuclei, the highest positive correlations existed between template-engaged RNA polymerase II, ovalbumin mRNA synthesis in vitro, and estrogen receptor concentration. Interestingly, restimulation of estrogen-withdrawn chicks results in replenishment of RNA polymerase II activity to prewithdrawal levels within 4 h; however, the recovery of the numbers of template-engaged polymerase II molecules, ovalbumin gene transcription, and nuclear receptor binding lags behind. These findings suggest that the estrogen effect on RNA polymerase activity is more rapid than the increase in template-engaged RNA polymerase II and ovalbumin-specific gene transcription. The excellent correlation that exists between nuclear estrogen receptor concentrations, template-engaged RNA polymerase II, and ovalbumin gene transcription strongly supports the hypothesis that estrogen receptors mediate RNA polymerase II binding to sequences associated with preferential transcription of the ovalbumin gene.