Acceptor proteins of rat prostate residual chromatin

The androgen acceptor sites of the rat prostate residual chromatin (2 M NaCl insoluble fraction of chromatin) have been determined by steroid exchange assay, binding of translocated androgen-receptor complex in vitro, and solubilization of the acceptor protein(s) from the residual chromatin. Binding of [3H]dihydrotestosterone to the residual chromatin was saturable, displaying high affinity (Kd = 3.1 nM) and low capacity (6.3 nmol/mg of protein). The binding of [3H]dihydrotestosterone by the residual chromatin was androgen specific, as shown by steroid competition experiments. Intrachromatin binding study of translocated 5 alpha-[3H]dihydrotestosterone-receptor indicated that the residual chromatin contained 31% of the total chromatin-bound androgen, thus representing one of the major chromatin-androgen binding sites. The results suggested the presence of acceptor molecules in the residual chromatin with which the androgen-receptor interacted. To ascertain this, the residual chromatin was extracted with phenol, and the phenol-solubilized protein(s) was (were) assayed for acceptor activity by interaction with [3H]dihydrotestosterone-receptor complex. Comparison of phenol-solubilized residual proteins from rat prostate, spleen, and chicken erythrocyte indicated that [3H]dihydrotestosterone-receptor complex bound tissue specifically to the prostate residual protein and that the interaction required the presence of DNA. The possible importance of the residual DNA was examined by reannealing with cloned cDNAs coding for the subunit components of prostatic binding protein, an androgen-regulated oligomeric protein in rat prostate. The rates of reassociation kinetics of the residual DNA with the cDNAs were faster than with total DNA, equivalent to a 3-fold enrichment in prostatic binding protein coding sequences. The high salt resistant residual chromatin acceptor(s) thus appear(s) to be preferentially associated with androgen-activated genes.