Acceptor sites for the oestrogen receptor in hen oviduct chromatin

Partially purified hen oviduct oestrogen receptors, charged with [³H]oestradiol, were shown to specifically bind in vitro to purified hen oviduct chromatin. Maximal binding occurred within 60 min at 0°C in a Tris buffer containing 0.1 M-KCl and 0.5 mM-phenylmethanesulphonyl fluoride. The binding of the [³H]oestradiol-receptor complexes to intact purified chromatin was saturable, whereas the receptor binding to hen DNA remained linear. Saturation was further demonstrated by the minimal acceptor binding of receptor charged with [³H]oestradiol plus 200-fold oestradiol compared with [³H]oestradiol receptors at equal [³H]oestradiol concentrations. Scatchard analysis of [³H]oestradiol-receptor binding to chromatin above DNA levels gave indications of high-affinity binding with a low capacity. Further, the nuclear binding was tissue-specific since the binding to hen spleen chromatin was negligible. To further uncover the specific acceptor sites, proteins were removed from hen oviduct chromatin by increasing concentrations of guanidine hydrochloride (1-7 M). Those residual fractions extracted with 3-7 M-guanidine hydrochloride had the highest acceptor activity (above DNA levels) with the peak activity uncovered by 5 M-guanidine hydrochloride. To further characterize the oestrogen-receptor acceptor sites, oviduct chromatin was bound to hydroxyapatite in the presence of 3 M-NaCl and then protein fractions were extracted sequentially with 1-7 M-guanidine hydrochloride. Each fraction was then reconstituted to pure hen DNA by reverse gradient dialysis. [³H]Oestradiol receptors were found to bind to the greatest degree to the fraction reconstituted from the 5 M-guanidine hydrochloride protein extract. Reconstituted nucleoacidic proteins (NAP) from combined 4-7 M-guanidine hydrochloride protein extracts showed saturable binding by [³H]oestradiol receptors, whereas binding to hen DNA did not saturate. The high affinity, low capacity, and specificity of binding of oestrogen receptors to NAP was similar to that found in intact chromatin. Thus, chromatin acceptor proteins for the oestrogen receptor have been partially isolated and characterized in the hen oviduct and display properties similar to that reported for the acceptor proteins of the prosgesterone receptor.