The present study was designed to determine the characteristics of the progesterone receptor and chromatin binding site (“acceptor”) of the progesterone-receptor complex in the rabbit uterus. The uterus was obtained from an estrogen-primed immature female rabbit. The binding of progesterone to the uterine receptor was examined in vitro. The progesterone-receptor binding was reduced only by proteases, and phosphorus moiety may not be related for progesterone-receptor binding.
The effects of enzymes on the acceptor of the chromatin were investigated. The progesterone-receptor complex was bound to the dehistonized chromatin. The dehistonized chromatins, which were pretreated with enzymes at 4°C or 37°C for 30 minutes, were incubated with 3H-progesterone prelabeled uterine cytosol at 4°C for 30 minutes, and the radioactivity in the chromatin pellet was counted.
Proteases effectively decreased the receptor binding capacity to the dehistonized chromatin in the following order : pronase>trypsin>papain>α-chymotrysin. DNAse moderately and phospholipase A slightly decreased its binding capacity. The results may indicate that the acceptor site of the progesterone receptor is nonhistone protein over DNA of chromatin and may contain phosphorus moiety.
