RNA inhibits estrogen receptor binding to DNA.

Cytosol from MTW9 rat mammary tumor contains a high molecular weight inhibitor of estrogen receptor binding to DNA. RNase treatment of crude preparations destroys inhibitory activity, whereas DNase or trypsin treatment are without affect, suggesting that some RNA molecule might be involved; in addition, RNA extracted from tumor cytosol was an effective inhibitor of estrogen receptor binding to DNA. A number of synthetic and natural RNA species were analyzed for inhibitory activity; a definite specificity was observed, with poly(G) > poly(U) > poly(A) or poly(C).