Ribosomes are ribonucleoprotein particles which process the genetic
information coded in mRNA into protein synthesis. The analogy in function
and composition of ribosomes from various sources, both prokaryotic and
eukaryo-tic, imply a structural similarity. At present, high resolution
electron microscopy is the most direct technique with a potential to resolve
the extent of the structural homology of ribosomal particles at a
macromolecular level.
The structure of ribosomes is highly complex as a result of the large
number of their constituents. In general, 80S eukaryotic monosomes consist
of two uneven subunits - large (60S) and small (40S) - accomodating four
different RNAs and approximately 80 different proteins. Mutual orientation
of both subunits on the monosome is of particular interest because it
determines the interface, the supposed site of interactions of ribosomes
with other macro-molecules involved in peptide bond formation. Since
entrapping of the contrasting solution (0.5% aqueous uranyl acetate)
obscures all structural details in the interface, information on its
architecture is limited to an indirect reconstruction based on the
established 3-D structure of both sub-units and their mutual position after
association.