The incorporation of adenine nucleotides into ribonucleic acid of cell-free systems from liver.

The isolation and purification of enzymes from bacteria that polymerize ribonucleoside diphosphates (l-3) have intensified the search for enzymes in animals that will synthesize RNA.l A number of reports (4-11) have established that radioactive compounds can be incorporated into RNA in cell-free systems from animals, but the pathway of incorporation and the identity of the immediate precursor of RNA remain in doubt. The role of subcellular fractions from rat liver in the incorporation of erotic acid-6-Cl4 int.0 RNA was studied by Herbert, Potter, and Hecht (10). It was found that the extent of incorporation is directly proportional to the concentration of microsomes in t,he presence of mitochondria and a soluble enzyme fraction. The mitochondria apparently supply energy for the incorporation, and the soluble enzyme fraction converts erotic acid to acid-soluble uracil nucleotides, the precursor pool from which the uridylic acid moiety of RNA is derived (12). The role of the nuclear fraction was not determined. The studies reported here are an attempt to clarify further the role of the cell fractions in the synthesis of RNA. P-labeled adenine nucleotides have been substituted for erotic acid in the hope that they would provide more immediate precursors of RNA.