Objectives: (a) Studies on mechanism of thyroxine-action on gene repression and derepression in amphibian metamorphosis of tadpole; this includes acetylation, methylation of nuclear proteins (histone and nuclear non-histone protein) in vivo and in vitro, and thyroxine-binding protein in the liver and tail. (b) Effect of various enzymes in modifying the amino acid side chains (protein methylase I, II, III, epsilon-lysine acylase, epsilon-N-acetyllysine synthetase as well as histone hydrolase). (c) Studies on the enzymatically altered proteins for changes in structure and function.