Ribonuclease-induced transformation of progesterone receptor from rabbit uterus

The effect of RNase on the transformation of progesterone receptor from rabbit uterus was studied by density-gradient centrifugation and DNA-cellulose binding assay. The 7S form of the receptor in crude cytosol was RNase sensitive, and converted to the 4S form after RNase treatment. This reaction was prevented by an RNase inhibitor and reversed by the addition of ribosomal RNA. RNase treatment also caused a two-fold increase in the DNA binding of cytosolic receptor, and reduced the time required for heat-induced transformation. However, sucrose-gradient-purified progesterone receptor (7S) did not undergo transformation by warming unless exogenous RNase was added, thereby suggesting that a cytosolic factor, which might be endogenous RNase, is necessary for the heat-induced transformation of progesterone receptor. Furthermore, degradation of the receptors which occurred after prolonged warming at 25 degrees C in the presence of RNase could be prevented by the addition of DNA-cellulose to the reaction mixture. These results indicate that RNA is associated with the 7S form of progesterone receptor, and that its hydrolysis by RNase might be involved in the transformation of this receptor.