Incorporation of amino acids by rat liver nucleoli in vitro

Isolated rat liver nucleoli are shown to incorporate radioactive amino acids into proteins. The characteristics of this nucleolar protein-synthesizine system indicated that the incorporation observed was not due to cytoplasmic or bacterial contamination. The products synthesized by isolated nucleoli have been analyzed by polyacrylamide gel electrophoresis and subsequent autoradiography; this revealed a few radioactive bands suggesting that in vitro only a few proteins are labelled. The results presented are discussed in view of a possible nucleolar protein synthesis.