R. Rendi
The Wenner-Gren Institute for Experimental Biology, University of Stockholm, Sweden
Nuclear fractions isolated from rat liver are able to incorporate labeled amino acids in vitro. Evidence is given that the incorporation mainly is into nuclear proteins. By fractionation of the protein after incubation of the intact preparations with the labeled amino acid, the residue not extractable in M NaCl was shown to be the most active fraction. The proteins of the DNA containing fraction were less labeled. The experiments strongly suggest that active RNP-particles are present in rat liver nuclei. No conclusive evidence could be obtained in support of the hypothesis that a second site for amino acid incorporation into proteins is present in the nuclei.
1. Frenster JH, Allfrey VG, and Mirsky AE, "Metabolism and Morphology of Ribonucleoprotein Particles from the Cell Nucleus of Lymphocytes", Proc. Natl. Acad. Sci. U.S.A. vol. 46, no. 4, pp. 432-444 (April, 1960).
2. Frenster JH, Allfrey VG, and Mirsky AE, " In Vitro Incorporation of Amino Acids into the Proteins of Isolated Nuclear Ribosomes", Biochim. Biophys. Acta vol. 47, pp. 130-137 (1961).