Association of the Uterine 17β-Estradiol-Receptor Complex with Ribonucleoprotein in Vitro and in Vivo

The 17β-[3H]estradiol-receptor complex prepared from the cytosol of calf uteri can form a ternary complex with either the 50 S or the 80 S ribonucleoprotein particles of the uterine cell nuclei. This association appears to be limited to a small proportion of the total nuclear ribonucleoprotein particles. Similar ribonucleoprotein particles that bind the estrogen-receptor complex are present in the cytoplasmic fraction, but the cytoplasmic monosome and polysome forms of ribosomes do not bind the estrogen-receptor complex firmly. Ribonucleoprotein particles dissociated from the monosomes and polysomes, however, can bind the estrogen-receptor complex. Escherichia coli ribosomal particles at similar concentrations do not have this receptor binding ability. The [3H]estrone-receptor complex also binds to the nuclear ribonucleoprotein particles, but to a much lesser extent than the 17β-[3H]estradiol-receptor complex. The [3H]progesterone-protein complex of the same tissue and the 5α-[3H]dihydrotestosterone-receptor complex of rat ventral prostate were ineffective. The association of the 17β- [3H]estradiol-receptor complex to the rat uterine ribonucleoprotein particles appears to occur also in vivo.