Binding of Nuclear Triiodothyronine (T3) Binding Protein-T3Complex to Chromatin

Abstract

Nuclear triiodothyronine (T3) binding protein (NTBP)-T3 complex, prepared from liver nuclei of rats given [125I]T3 in vivo, rebinds to rat nuclear chromatin at pH 7.4 and at low, but not high, KCl concentrations. Liver NTBP-T3 complex binds to chromatin from liver, kidney, heart, brain, testis and spleen. Binding was depressed at pH 8, by addition of 10 mM CaCl2 or 100 mM MgCl2 and by 1 mM GTP or UTP. Although heart chromatin bound the most NTBP-T3 complex and brain the least, there is no clear separation of binding activity on comparison of 3 T3-responsive tissues (heart, liver, kidney) to the T3 insensitive tissues. Under the conditions of these experiments, there was no evident competition for binding sites on any of the 6 chromatins tested.