Tsai S Y, Tsai M J, Schwartz R, Kalimi M, Clark J H, O'Malley B W
Proc Natl Acad Sci U S A. 1975 Nov;72(11):4228-32. doi: 10.1073/pnas.72.11.4228.
Estrogen (diethylstilbesterol) was administered in vivo to chicks for various time periods. Chromatin was then prepared from oviduct nuclei and assayed for its capacity to support initiation of RNA chain synthesis in vitro in the presence of saturating levels of Escherichia coli RNA polymerase (RNA nucleotidyltransferase; nucleosidetriphosphate:RNA nucleotidyltransferase; EC 2.7.7.6). These same nuclei were also assayed by a [3H]estradiol exchange assay for their endogenous receptor content. The number of available initiation sites for RNA synthesis on chromatin was shown to correlate with the endogenous levels of nuclear estrogen receptor. A decrease in the nuclear concentration of estrogen receptor molecules and the concentration of initiation sites for RNA synthesis occurred during withdrawal of estrogen from previously stimulated chicks. Both parameters declined with a similar half-life. When estrogen was readministered to withdrawn chicks, the number of initiation sites increased 2-fold as early as 30 min and approached a maximal level (3-fold) by 1 hr. During the same period of restimulation with estrogen, the number of estrogen receptor molecules bound to nuclei increased to a maximum at 20 min and then declined at 1 hr to a steady-state level 2-fold higher than the withdrawn chicks. Simultaneous measurements of RNA chain length and RNA chain propagation rate demonstrated that parameters remained relatively constant throughout estrogen withdrawal as well as secondary stimulation. The temporal correlation between changes in the levels of nuclear-bound estrogen receptor and the number of RNA chain initiation sites on chromatin prepared from these same nuclei strongly suggested that the hormone receptor complexes act on chromatin to mediate these changes in genetic transcriptional activity.
将雌激素（己烯雌酚）在体内给予雏鸡不同时间段。然后从输卵管细胞核制备染色质，并在存在饱和水平的大肠杆菌RNA聚合酶（RNA核苷酸转移酶；核苷三磷酸：RNA核苷酸转移酶；EC 2.7.7.6）的情况下，测定其在体外支持RNA链合成起始的能力。这些相同的细胞核也通过[3H]雌二醇交换试验测定其内源性受体含量。结果表明，染色质上RNA合成的可用起始位点数量与核雌激素受体的内源性水平相关。在先前受到刺激的雏鸡停止给予雌激素期间，雌激素受体分子的核浓度和RNA合成起始位点的浓度均下降。这两个参数均以相似的半衰期下降。当对停止给予雌激素的雏鸡重新给予雌激素时，起始位点数量早在30分钟时就增加了2倍，并在1小时时接近最大水平（3倍）。在雌激素重新刺激的同一时期，与细胞核结合的雌激素受体分子数量在20分钟时增加到最大值，然后在1小时时下降到比停止给予雌激素的雏鸡高2倍的稳态水平。对RNA链长度和RNA链延伸速率的同时测量表明，在整个雌激素撤离以及二次刺激过程中，这些参数保持相对恒定。核结合雌激素受体水平的变化与从这些相同细胞核制备的染色质上RNA链起始位点数量之间的时间相关性强烈表明，激素受体复合物作用于染色质以介导遗传转录活性的这些变化。
