Identification and metabolic relationship between the protein moieties of nucleolar 60-S particles and of ribosomal large subunits of rat liver were investigated by means of two-dimensional poly-acrylamide gel electrophoresis.

  • 1
    Cytoplasmic ribosomal large subunits showed 36 major protein spots (C1– C36) on the gel. Similar patterns as a whole were obtained in the case of the nucleolar 60-S particles of thio-acetamide-treated rat liver, although four major proteins (N1–N4) and a number of minor proteins were specific for nucleolar particles and some proteins including three major ones (C8, C20 and C31) for ribosomal large subunits.
  • 2
    Gel electrophoresis of the mixture of proteins of large subunits labeled in vivo with 3H-labeled amino acid mixture for 4 h and those of nucleolar 60-S particles labeled with 14C-labeled amino acid mixture for 15 min, both of which were prepared from regenerating rat liver, showed 33 major protein spots having both 3H and 14C radioactivities. While C8, C23 and C31 proteins specific for cytoplasmic ribosomal large subunit showed only 3H radioactivity, proteins specific for nucleolar particles had negligible 14C radioactivity. It was further found that at least two of these three proteins (C20 and C31) were rapidly labeled in vivo when compared with other proteins of the large subunits.