Microsomal Protein Synthesis in the Isolated Perfused Liver during Actinomycin Blockage of RNA Synthesis

Abstract

IN mammalian tissues the mRNA template for protein synthesis has been found to be fairly stable in contrast to that in the microbes^1–3. An average half life of 2 h was demonstrated for the liver mRNA in steady state conditions⁴. Study of the cessation of protein synthesis after treatment with actinomycin, however, showed variable results. Even a very large dose of actinomycin could not affect the protein synthesis of the liver slices in contrast to that of the cell free system⁵. In some cases, the in vitro microsomal protein synthesis was also unaltered⁶ although the actinomycin gradually decreased the ^{in vivo} protein synthesis⁷. A correlation has been demonstrated between the decay of mRNA and the cessation of the in vitro protein synthesis while RNA synthesis was blocked by actinomycin showing 8–12 h (ref. 8) and 1 h (ref. 9) to be an average half life for the liver messenger. Our own work was stimulated by conflicting reports of the effect of actinomycin on protein synthesis in the liver. We have measured the protein synthesis and changes in the messenger receptor sites in a cell free system obtained from isolated perfused liver to which actinomycin had been added.