The role of cytoplasmic ribonucleic acid in the incorporation of amino acids into microsomal proteins

Abstract

The incorporation of amino acids into the ribonucleic acid (RNA) of the fraction of the cell sap precipitated at pH 5.2 (pH 5 fraction) of liver, spleen and lymphosarcoma was studied. Alanine was incorporated to the same extent into liver and spleen preparations, whereas leucine was more actively incorporated into liver pH 5 RNA. Dilution of the pH 5 fraction enhanced the incorporation of amino acid into pH 5 RNA. If the cell sap was fractionated by the method of Sachs, which involves the removal of a precipiate formed by the addition of protamine, a fraction was obtained (S-protein) which promoted the incorporation of amino acid into microsomal protein. S-Protein contains no more than traces of RNA. When pH 5 RNA was added to S-protein the ability of this fraction to promote the incorporation of amino acid into microsomal protein was enhanced. Under these conditions amino acids were incorporated into pH 5 RNA. Incorporation of leucine into microsomal protein in the presence of non-dialyzed S-protein was not enhanced by glutathione. The reverse was true if dialyzed S-protein was used. Although the addition of liver pH 5 RNA to liver S-protein enhanced the incorporation of amino acids into liver microsomes, spleen pH 5 RNA had an inhibitory effect.