THYROXINE STIMULATION OF AMINO ACID INCORPORATION INTO PROTEIN INDEPENDENT OF ANY ACTION ON MESSENGER RNA SYNTHESIS

Abstract

Thyroxine added in vitro to cell-free rat liver preparations stimulates amino acid incorporation Into protein in the absence of any effect on the incorporation of RNA precursors into RNA. The thyroxine stiulation is superimposed on the effects of optimal or greater than optimal amounts of nuclei containing RNA polymerase activity and messenger RNA. Inhibition of DNA-dependent RNA polymerase activity by actinomycin D and DNAase has no effect on the control rate of amino acid incorporation into protein or the thyroxine effect Thyroxine also stimulates the rate of poly U-directed incorporation of phenylalanine into polyphenylalanine. These results are interpreted to indicate that thyroxine stimulates amino acid incorporation into microsomal protein independently of any action on DNA-dependent RNA polymerase activity or messenger RNA synthesis.