Studies on the distribution of ribosomal proteins in mammalian ribosomal subunits

Murine L5178Y cell ribosomes were dissociated into subunits either with potassium chloride in the presence of puromycin or with the chelating agent EDTA. The proteins of ribosomal subunits obtained by these different methods were compared by means of bidimensional polyacrylamide gel electrophoresis. KCl-derived 60S and 40S subunits were shown to contain 38 and 31 proteins respectively, 3 of them having identical electrophoretic mobilities. Preparations of EDTA-dissociated ribosomal subparticles contained different proportions of these proteins, and 11 major spots were shared between the EDTA-derived large and small ribosomal subunits. Furthermore, 10 proteins absent from subunits treated by high concentrations of KCl were reproducibly found in EDTA-treated ribosomal subparticles.