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

Thyroid Study Unit, Department of Medicine, University of Chicago Chicago, Illinois

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, KC1 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 three 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 six chromatins tested.

Footnotes

Supported by United States Public Health Service Grants AM-13,377 and CA-14,599.

Received February 10, 1976.