3,5,3'-triiodothyronine receptor-containing chromatin fragments: production by nuclease digestion.

Nuclear thyroid hormone (T3) receptors are nonhistone proteins which are tightly bound to rat liver chromatin. The solubilization of the T3 receptors by micrococcal nuclease was studied using an assay which allows the delection of in vitro hormone binding and which is independent of the state of solubility of the chromatin. Nuclease digestion produces a receptor containing moiety which sediments at a rate of 5--6S. This form of the receptor is different than that released from chromatin at high ionic strength (3.8S) and potentially represents the stable association of the receptor which other elements of chromatin. Partial release of chromatin compaction by the use of dilute buffer solutions increases the rate of nuclease digestion, facilitates the release of the (5--6S) T3-receptor complex, and allows the isolation of sucrose gradient fractions which are enriched with receptor.