Studies on the Protein Moiety of Plant Ribosomes ENUMERATION OF THE PROTEINS OF THE RIBOSOMAL SUBUNITS AND DETERMINATION OF THE DEGREE OF EVOLUTIONARY CONSERVATION BY ELECTROPHORETIC AND IMMUNOCHEMICAL METHODS

Abstract The approximate number and molecular weight of pea seedling ribosomal proteins were determined by two-dimensional electrophoresis on polyacrylamide gels containing either urea or sodium dodecyl sulfate. The small (40 S) ribosomal subunit contained 32 to 40 proteins and the large (60 S) subunit 44 to 55 proteins. The great majority of ribosomal proteins were basic and had molecular weights between 20,000 and 30,000. At least two proteins of higher molecular weight were found in the large subunit. Structural homologies between ribosomal proteins of different origin were estimated by two-dimensional electrophoretic analysis, by immunoelectrophoresis, double-diffusion tests, and quantitative immunoprecipitation. A high degree of evolutionary conservation was found, by the above methods, among ribosomal proteins of several species of higher plants, whereas little homology was found between chloroplast proteins and cytoplasmic ribosomal proteins of the same plant. No homologies were detected between chloroplast ribosomal proteins and proteins extracted from ribosomes of either mitochondria, bacteria, or blue-green algae.