Ribosomes contain one large and one small subunit and are characterized by the rate of sedimentation and their names are derived from the sedimentation coefficients in Svedberg units. Prokaryotes contain the small and large subunits called 30S and 50S, which are combined to form 70S, whereas in eukaryotes 40S and 60S subunits associate to form 80S.
But, it is unsure that a chimeric translation system containing large ribosomal subunit from Escherichia coli and small ribosomal subunit from a unicellular eukaryote like yeast to function in protein synthesis. Even though the steps of translation and the mechanism of ribosomes are similar in both prokaryotes and eukaryotes, but the ribosomes are not identical. Compared to the size of ribosomes in prokaryotes, the both subunits in eukaryotes are larger and possess definite and complex interactions that should occur between the small and large subunits, which are not achievable in chimeric system.