[RNA synthesis and modifications of heart nuclear proteins during thyroid hormone deficiency].

RNA synthesis, correlation of various histones and acetylation and phosphorylation of the chromatin proteins were studied in the rat heart during monthly hypothyroidism. It was shown that [3H]uridine incorporation into heart RNA decreases considerably at hypothyrosis. The alteration in relative amounts of the histone H4 subfractions, which does not depend on the method of hypothyrosis reproduction (inhibition of thyroid function by 1-methyl-2-mercaptoimidazole, thyroidectomy) was detected by the method of analytical electrophoresis in 15% polyacrylamide gels containing 3.125 M urea and 0.9 N acetic acid. Increased incorporation of [32P]phosphate into histone fraction H2b and total fraction of acidic chromatin proteins was observed in vivo. Increased incorporation of labeled acetate into the total histone fraction and reduced incorporation into acidic nuclear proteins were obtained. It was shown that the increased incorporation of acetate into the total histone fraction was due to the increased acetylation of histones H3, H2b, H4 and acid-soluble chromatin proteins characteristic of tissues with a low level of replication. It is assumed that the observed changes of nuclear proteins reflect the process of chromatin reorganization caused by a prolonged deficiency of thyroid hormones.