Evidence for major differences in ribosomal subunit proteins from Plasmodium berghei and rat liver

Purified polysomes were isolated in high yield from the erythrocytic stages of the rodent malaria parasite, Plasmodium berghei, and from rat liver. Proteins extracted from the ribosomal subunits derived from these polysomes were fractionated and their number and molecular weights were estimated by two-dimensional polyacrylamide gel electrophoresis. Plasmodial small ribosomal subunits contained 30 proteins ranging in apparent molecular size from 11.7 to 40.7 kDa, while large subunits contained 35-36 proteins ranging from 12.1 to 42.6 kDa. None of these parasite proteins was shared by the two subunits nor altered in electrophoretic mobility by radioiodination. Rat liver 40 S ribosomal subunit proteins numbered 30 and ranged from 9.2 to 37.5 kDa, while liver 60 S subunits contained 41-43 proteins with apparent molecular sizes of 10.3-45.2 kDa. Coelectrophoresis of trace amounts of radioiodinated P. berghei ribosomal subunit proteins and stainable quantities of liver proteins demonstrated that most of these 139 parasite and host ribosomal proteins possessed different two-dimensional electrophoretic mobilities under the conditions of this study. Based upon a comparative analysis of P. berghei and rodent ribosomal RNA and these data, it was concluded that parasite and host ribosomes contain distinct ribosomal RNAs and ribosomal proteins.