Mechanisms controlling steroid receptor binding to specific DNA sequences

Mammalian progesterone receptors activated by hormone binding in nuclei of intact cells exhibit substantially higher binding activity for specific DNA sequences than receptors bound with hormone and activated in cell-free cytosol. Differences in DNA-binding activity occur despite the fact that both activated receptor forms sediment at 4S on sucrose gradients and are apparently dissociated from the heat shock protein 90. This suggests that hormone-induced release of heat shock protein 90 from receptors is necessary, but not sufficient for maximal activation of DNA binding. This report is a review of studies from our laboratories that have examined the role of receptor interaction with other nuclear protein factor(s), and receptor dimerization in solution, as additional regulatory steps involved in the process of receptor activation and binding to specific gene sequences.