The nuclear binding of estradiol stimulates ribonucleoprotein transport in the rat uterus

An inverse relationship exists in the rat uterus between the endogenous estradiol concentration and the rate of accumulation within the nuclei of ribonucleoproteins (RNP) that bind estradiol. Exposure of the uterine nuclei to physiological concentrations of estradiol, either in vivo or in vitro, results in the hormone binding to the nuclear RNP and the transport of the RNP-estradiol complex from the nuclei. Evidences suggest that the RNP-estradiol complex, thus released upon in vivo exposure of the nuclei to estradiol, associates with the ribosomes forming polysomes. The polysome profiles show that the hormone-binding activity is mainly associated with the rapidly sedimenting polysomal fractions.