Characterization of ‘native’ and ‘activated’ progesterone and oestrogen receptors from chick oviduct cytosol

Soon after the discovery, in the cytosol of mammalian uterus, of specific oestrogen-binding proteins termed ‘receptors’ (Talwar et al., 1964, Toft et al., 1967; Baulieu et al., 1967), it was established that exposure of the tissue to oestradiol in vivo or at 25–30°C in vitro leads to a rapid shift of the receptor-hormone complexes to the nuclear compartment (Jensen et al., 1968; Gorski et al., 1968). It was also found that, in cell-free systems, this ‘translocation’ of the receptor-oestradiol complexes from cytosol to the nucleus also can be obtained by incubation at 25–30°C, and that upon warming at this temperature of cytosol oestradiol-receptor complexes, a change of the sedimentation coefficient takes place (initially ~ 4S in 0.3 M KCl containing buffer, it becomes ~ 5S), while they acquire the ability to bind to nuclei (Jensen et al., 1971). Detailed studies with other receptor-steroid complexes have shown that this ‘transformation’ or ‘activation’ can be obtained in all cases, and that it results in increased binding not only to nuclei but also to DNA and to certain other polyanions (Higgins et al., 1973; Milgrom et al., 1973), although the changes in observable physico-chemical parameters due to activation vary with the hormone and with the species (see, for example, reviews by Baulieu et al., 1975; Gorski and Gannon, 1976; Katzenellenbogen, 1980, Simmons, 1980).