The intranuclear distribution of rat uterine estrogen receptors determined after nuclease treatment and chromatin fractionation

Binding of the glucocorticoid receptor complex to the nucleosomal core in the P1798 mouse lymphosarcoma

Binding of the glucocorticoid receptor complex to nucleosomes has been studied using the mouse P1798 lymphosarcoma. Cells were incubated with [3H]triamcinolone acetonide (TA), and nuclei prepared and digested with 3 different concentrations of micrococcal nuclease. After fractionation with EDTA and NaCl, it was observed that [3H]TA bound with similar specific radioactivity to mononucleosomes containing both core and linker DNA, of 183 +/- 5, and 168 +/- 4 base pair lengths, respectively, as well as to core size DNA, of 148 +/- 3 base pair length, suggesting that the glucocorticoid receptor bound to the core portion of the nucleosome. Steroid binding was found to be associated with regions of the nucleosome that were depleted in histone H1 and enriched in high mobility group (HMG) proteins 1 and 2; only negligible binding was noted in nucleosomes enriched in histone H1 and depleted in HMG proteins. In addition to binding to core nucleosomes, the glucocorticoid receptor complex was also shown to bind to a fraction sedimenting at 5-6 S on sucrose gradients characterized by subnucleosome and mononucleosome size DNA, as well as by core histones. While binding of the steroid receptor complex to linker regions of the nucleosome cannot be ruled out, this data would appear to present the first concrete evidence that glucocorticoid binding, at least in the P1798 lymphosarcoma, is to core nucleosomes. Some caution in interpretation of the results is indicated, however, on 2 points: (1) receptor redistribution during nuclease digestion cannot be ruled out; (2) only the binding of a small proportion of the steroid receptor complex may be physiologically relevant.

A study of the androgenic function of the epididymis

Rats were subjected to bilateral orchidectomy or orchido - epididymidectomy and maintained on either 500 micrograms testosterone or testosterone propionate daily. The ventral lobes of the prostate were subsequently excised and examined for androgen receptors in terms of the total present in the cytosol and the nucleus, the proportion unoccupied by endogenous androgen and the relative populations that were nuclease excisable or nuclease resistant in the two groups of animals. A further group of animals was subjected to unilateral deferential venotomy and the same parameters examined in the ipsi- and contra-lateral lobes of the ventral prostate and the seminal vesicles. In the absence of the epididymides there was a reduction in the number of receptors per prostatic cell and an increase in the proportion that were unoccupied. The nuclei from these glands contained fewer receptors than did those from the animals in which the epididymides had not been excised. The effect of unilateral deferential venotomy was to bring about a relative increase in the number of cytoplasmic receptors in the ipsilateral lobes of the ventral prostate with a much greater proportion unoccupied compared with the lobes contra-lateral to the ligation. There was again an increase in the proportion of nuclease-sensitive receptors in the nuclei ipsilaterally. The conclusions are that the absence of the epididymides in androgen-maintained rats or deferential venotomy induces a relative androgen- deficiency of the prostate and seminal vesicles as reflected in the androgen receptor populations of these organs.