Fractionation of chromatin into urea-soluble chromosomal nonhistone proteins (UP), histones (HP), and DNA-associated nonhistone proteins (NP) revealed that the NP fraction from testicular and prostatic chromatin contains organ-specific acceptors for complexes of 5a-dihydrotestosterone (17j3-hydroxy-5a-androstan-3-one) and its receptor. This acceptor capacity of androgenic tissue chromatin could be transferred to chromatins from non-target tissues with the NP fraction of DNA-associated proteins. Phosphorylation of chromatin enhanced its hormone-receptor binding capacity. According to current views, early steps in the action of steroid hormones on their target tissues involve the association of the steroid hormone with cytoplasmic receptor, transport of this complex from cytoplasm into the nucleus, and, finally, its association with specific acceptor sites on chromatin (1-4). This association alters the transcriptional controls and allows the synthesis of new mRNA species. The new mRNAs are eventually translated into new proteins that are often specific for the hormone-stimulated tissue (1,3,5,6). The target cell nuclear acceptor is selective in that the nuclei of responsive cells accept more hormone-cytosol protein complex than the nuclei of tissues refractory to the action of steroid hormones (7,8). Recent years have seen the accumulation of considerable information concerning the steroid hormone-cytoplasmic receptor interactions in different types of tissue. After the hormone interacts with cytoplasmic receptor, the hormone-protein complex moves to the nucleus, where it is incorporated into chromatin. Liao and Fang (1) coined the term "acceptor protein" for the nuclear acceptor molecule. The acceptor protein fraction was isolated from prostate (9) and found to be heat labile and tissue specific, and could be transferred from the chromatin of one tissue to another with the fraction of chromosomal nonhistone proteins (3, 7). We report here the results of our studies on chromatin acceptor(s) in rat prostate and testis. MATERIALS AND METHODSProstatp, testis, liver, and pancreas from male Sprague-Dawley rats (125-150 g) were homogenized in ice-cold 0.25 M sucrose, 5 mM MgCl2, and 2 mM 2-mercaptoethanol in 20 mM Tris-HCI buffer, pH 6.8. The homogenate was centrifuged at 800 X g for 10 min. The crude nuclear pellet was purified by rehomoAbbreviations: SSC, standard saline citrate (150 mM NaCl, 15 mM sodium citrate); UP, chromosomal nonhistone proteins soluble in urea at low ionic strength; HP, histones; NP, DNA-binding chromosomal nonhistone protein fraction; DHT, 5a-dihydrotestosterone (17f,-hydroxy-5a-androstah-3-one). After incubation with labeled hormone, the cytosol-hormone complex was fractionated with (NH4)2SO4 (0-33% saturation). The active fraction was freed from unbound hormone by gel -filtration on a Sephadex G-25 column (1 X 24 cm). Sucrose density gradient analysis of the purified [3H]DHT-receptor complex showed that essentially all the radioactivity was associated with the receptor protein peak ...