Modification of the template capacity of chick-oviduct chromatin for form-B RNA polymerase by estradiol.

Abstract

1 Within 2 h of administration of estradiol in vivo to immature chickens, ENA synthesis by both form A and B RNA polymerases is stimulated in isolated oviduct nuclei. 2 24 h after hormone treatment this effect is enhanced, and is accompanied by four- and two-fold increases in the level of extractable form A and B enzymes in the nucleus. 3 The endogenous RNA polymerase activity associated with nuclear chromatin is also stimulated by estradiol. 90% of this activity, as shown by the use of the drugs α-amanitin and rifampicin AF/0–13, represents from B enzymes elongating RNA chains. 4 Analysis of RNA chains synthesised by the endogenous RNA polymerases of chromatin from estradiol-treated animals (E-chromatin) or control animals (C-chromatin) indicates that there is 2 to 3-times the number of elongating RNA chains in E-chromatin than in C-chromatin. 5 E-chromatin is twice as efficient as template for purified hen magnum form B RNA polymerase compared with C-chromatin. Two independent methods demonstrate that this effect is not due to differential ribonuclease content in the chromatins. 6 The results suggest that at early times during the differentiation of oviduct cells by estradiol the chromatin template is modified, thus providing additional binding sites for RNA polymerase molecules.