Rat liver mitochondrial aspartate aminotransferase mRNA: synthesis of an higher molecular weight precursor by free polysomes.

The site of synthesis of the higher molecular weight precursor of mAAT has been determined by separation of free and membrane-bound polysomes. Free and bound polysomes were isolated from rat liver and the polyA+RNA was extracted. Protein synthesis was carried out for two hours by using a reticulocyte lysate system in the presence of 35S-methionine. The samples were subjected to immunoprecipitation with specific antiserum. The precipitates were analyzed by Na-DodSO4/polyacrylamide gel electrophoresis and fluorography. The results clearly demonstrate that the enzyme is synthesized by free polysomes.