Similarity in the size and number of ribosomal proteins from different prokaryotes

The ribosomal proteins from nine species of prokaryotes have been compared by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The stained gels were scanned spectrophotometrically, the weight and number average molecular weights were calculated, and the detailed distribution of the proteins as a function of molecular weight was determined. By all of these criteria, the ribosomal proteins from all the species closely resembled each other, despite differences in the pattern of protein bands by conventional disc-gel electrophoresis. Therefore, it is suggested that the structural requirements for the assembly of ribosomal subunits have imposed limitations on the evolution of the ribosomal proteins and that their size has been highly conserved.