Image analysis of Artemia salina ribosomes by scanning transmission electron microscopy

A dedicated scanning transmission electron microscope (STEM) at Brookhaven National Laboratory was used to visualize unstained freeze-dried ribosomal particles under conditions which considerably reduce the specimen distortion inherent in the heavy metal staining and air-drying preparative steps used in routine transmission electron microscopy (TEM). From high-resolution STEM images it is possible to determine molecular mass and the mass distribution within individual ribosomal particles and perform statistical evaluation of the data. Analysis of digitized STEM images of Artemia salina ribosomes provided evidence that a standard preparation of these eukaryotic ribosomes consists of a population of heterogenous particles. Because of the integrity of rRNAs established by agarose gel electrophoresis, variations in the composition and structure of the 80S monosomes and the large (60S) and small (40S) ribosomal subunits, as monitored by their mass, were attributed to the loss of ribosomal proteins, from the large subunits in particular. These results are relevant not only to the degree of ribosomal biological activity, but should also be taken into consideration for particle selection in the reconstruction of the "native" eukaryotic ribosome 3-D model.