[Oestradiol receptors in the calf uterus. Stimulation of RNA biosynthesis in vitro].

Abstract Oestradiol receptors in the calf uterus. Stimulation of RNA biosynthesis in vitro 1. 1. Cytoplasmic and nuclear oestradiol receptor proteins were prepared from calf uterine endometrium. 2. 2. The cytoplasmic hormone-receptor complex was studied by analytical ultracentrifugation at different ionic strengths. A sedimentation coefficient of 7.7 S was obtained at low ionic strength. At higher ionic strengths a value of 5 S was obtained. It was shown that the bound oestradiol is associated with the 7.7-S and 5-S protein peaks. 3. 3. The incorporation of [5- 3 H]UTP into RNA by nuclei isolated from calf uterine endometrium was stimulated by the cytoplasmic 5-S receptor complex and also by a nuclear hormone-receptor complex, but not by the 7.7-S complex. 4. 4. Two enzyme fractions containing RNA polymerase activity were isolated from calf uterine endometrium. The “total RNA polymerase” fraction was stimulated by the cytoplasmic 5-S receptor complex, while the “soluble RNA polymerase” fraction was slightly inhibited. 5. 5. A hypothesis is presented concerning the mechanism of action of oestrogen at the level of the uterine endometrium.