Studies on Ribonucleic Acid Synthesis in Tadpole Liver during Metamorphosis Induced by Thyroxine: I. RELATION OF SYNTHESIS OF RIBONUCLEIC ACID AND OF CARBAMYL PHOSPHATE SYNTHETASE

Abstract

Abstract Liver of tadpoles exposed to thyroxine shows a biphasic pattern of ribonucleic acid synthesis, with an initial sharp peak appearing after 36 to 48 hours. This is followed by a gradual increase during the period 6 to 15 days later. An induction of carbamyl phosphate synthetase was observed when tadpoles were treated with thyroxine for 2 days. The maximum specific radioactivity of RNA was seen in the microsomal RNA fraction 2 days after thyroxine treatment. Actinomycin D inhibited RNA synthesis in liver at all the stages of metamorphosis induced by thyroxine; however, delayed administration of actinomycin D did not inhibit induction of carbamyl phosphate synthetase. In the later stages of metamorphosis, temperature-dependent (thyroxine-independent) carbamyl phosphate synthetase synthesis was observed accompanied by a rapid RNA turnover.