DNA-DEPENDENT RNA POLYMERASE I AND II ACTIVATION BY 17β-ESTRADIOL-RECEPTOR COMPLEX ON LIVER CHROMATIN FROM IMMATURE CHICKS

ABSTRACT In liver nuclei from immature chicks pretreated with 17β-estradiol for 24 hours (E 24 ) the endogenous RNA polymerase I and II activities were increased by more than 100% over that found in controls (C). In chromatin preparations from C and E 24 nuclei the difference in endogenous activities was still present but amounted to only 40%. Similarly, after solubilization of the RNA polymerases from C and E 24 nuclei, the majority of the difference in activity was lost. The loss was thought to be due to rupture by sonication of a defined structural configuration associated with chromatin. Chromatin E 24 contained estrogen receptor, chromatin C could be saturated with estrogen receptor: under these conditions the endogenous RNA polymerase activity was enhanced more than could be achieved with E 24 chromatin or E 24 nuclei. However, when the receptor was added to salmon sperm DNA together with solubilized polymerase, the effect was greatly diminished. In conclusion, the chick liver RNA polymerases seem to be activated by the estrogen receptor and this activation specifically requires homologous chromatin.