Interaction of oestrogen and progesterone receptors with specific subfractions of laying-hen oviduct chromatin.

Salt (NaCl)-extracted nuclear oestrogen receptor from hen oviduct was incubated with salt-depleted oviduct chromatin and dialysed to low salt. The oestrogen receptor (re)associated with chromatin to form a 13-14S-sedimenting fraction, as found in 'native' chromatin, and saturation of this interaction was obtained for very low receptor concentrations (approx. 0.04 nM). Similarly, purified progesterone receptor from chick oviduct cytosol associated with depleted chromatin to form an 11-12S-sedimenting fraction, as in 'native' chromatin; this interaction tended towards saturation for much higher concentrations of progesterone receptor (approx. 8 nM) than that observed for oestrogen receptor. When the two receptors were incubated with depleted chromatin from hen kidney or erythrocytes, their s values were as for oviduct chromatin. However, no saturation of these interactions was seen, even for high concentrations of receptor. Steroid-hormone receptors can therefore bind in vitro to particular subfractions of non-target-tissue chromatin, but with a much lower affinity than to target-tissue chromatin.