Thyroid hormone dependent nuclear proteins from rat liver

Two nuclear proteins from rat liver were shown to be dependent on thyroid hormones. These proteins were present in the nucleosol or nucleoplasmic fraction, and were extracted from the nuclei with 0.15 M NaCl at pH8. After thyroidectomy, a 120000-Mr polypeptide decreased in concentration to levels below 10% of normal control rats and another polypeptide of 81000-Mr was increased. Treatment with T4 at physiological replacement doses for several days restored the levels of both proteins to normal. A single administration of 50 micrograms T3 induced a detectable increase of 120K after 14 h, with maximal effects at 48 h after administration. The minimum effective dose of T3 on 120K as 0.5 microgram administered for three days. Preliminary observations suggest that the response of 81K to thyroid hormones is much more sensitive than that of 120K. The physiological role of these polypeptides is unknown, but they could be involved in the mode of T3 action at the nuclear level.