Regulation of Rna Synthesis in Isolated Nucleoli by Histones and Nucleolar Proteins.

distribution of label in the IEA patterns of the SON fractions was not affected by the addition of serum carrier, it seems unlikely that nonspecific binding of radioactive material to serum proteins occurs to any appreciable extent. There is the possibility that highly radioactive material in the SON fraction migrating with the same electrophoretic mobility is trapped and concentrated in the immune precipitate. This is unlikely, however, because of the dynamics of diffusion and precipitation in gels. Since incubation mixtures contained cell sap fractions from normal liver only, the differences observed in the labeled proteins were due to the modified capacity of the microsomal fraction to direct the synthetic activity. The striking differences between the labeled IEA patterns of cell-free systems obtained from normal and staphylococcus-infected mice closely parallel the differences observed in vivo5 and in vitro.3 We conclude, therefore, that under suitable conditions, cell-free systems reflect the activity of intact tissues.