Characterization of nuclear acceptor sites for mammalian progesterone receptor: comparison with the chick oviduct...

We performed binding studies with hamster uterine progesterone receptor (Rp) and various chromatin-cellulose preparations to determine whether Rp acceptor sites exist in mammalian uterus analogous to those observed in the chick oviduct. Chick and hamster Rp acceptor site assays were done according to the method of Spelsberg et al. [(1983) Recent Prog. Horm. Res. 39, 463-513]. Hamster Rp bound to hamster uterine chromatin-cellulose, NAP-cellulose (a 4 M guanidine hydrochloride-extracted fraction) and DNA-cellulose in a manner similar to that observed in the chick oviduct. Hamster Rp binding was tissue specific as evidenced by higher Rp binding to target-tissue vs non-target-tissue chromatin. The greatest degree of Rp binding occurred in the NAP fraction, and the higher level of binding seen in NAP-chromatin as compared with that in crude chromatin may be attributed to extraction of "masking proteins" which inhibit Rp-chromosomal protein interactions. When guanidine hydrochloride at greater than 4 M was used to extract crude chromatin, Rp binding decreased, indicating that the Rp acceptor sites were removed or denatured. These findings demonstrate the existence of Rp acceptor sites in the mammalian uterus which are similar to avian oviduct acceptor sites, suggesting that such sites may play a role in mediating Rp-induced gene expression.