Effect of ribosomal proteins on synthesis and assembly of preribosomal particles in isolated rat liver nuclei.

Ribosomal proteins are rapidly taken up by isolated rat liver nuclei. The proteins are localized mainly in the nucleolus and are found associated with a nucleolar 80 S particle containing newly synthesized 45 S RNA. Ribosomal proteins in the nucleoplasm were associated with particles containing 18 and 28 S RNAs. In the absence of ribosomal proteins in the incubations, there was a decrease in the amount of newly synthesized 45, 18, and 28 S RNAs and an increase in low molecular weight RNA in both the nucleolus and nucleoplasm. This in vitro system appears to be useful for studies on the formation of ribosomal particles in the nucleus.