Abstract
The distribution of newly formed ribosomal proteins between cytoplasmic, nucleoplasmic and nucleolar fractions of HeLa [human cervical cancer] cells was determined. All but a few of the newly formed ribosomal proteins were concentrated 10- to 50-fold in the nucleolus and 2- to 5-fold in the nucleoplasm. Substantial amounts were found in the cytoplasma. Pretreatment of cells with actinomycin D to deplete the nucleolar pool of ribosomal precursor RNA had no effect on the concentration of newly formed ribosomal proteins in the nucleus, but did lead to an increased amount in the nucleoplasm at the expense of the nucleolus.