Architecture of the Escherichia coli ribosome as determined by immune electron microscopy.

Binding sites for antibodies specific to nineteen of the twenty-one ribosomal proteins from the 30S subunit of E. coli ribosomes have been localized on the surface of the 30S ribosomal subunit by immune electron microscopy. The locations of 13 ribosomal proteins from the 50S subunit were similarily assessed. The arrangement of these proteins is illustrated in three-dimensional models of the 30S and 50S ribosomal subunits and of 70S ribosomes. With specific antibodies to six proteins of the 30S subunit we found only one attachment point for each protein. Antibodies against each of nine of the proteins attached at two separate sites that were separated by various distances. Four further proteins were exposed at three or four sites for antibody binding. Altogether eight to ten of the 19 proteins of the 30S subunit have shown antibody attachment sites at remote points on the surface of the ribosome, at distances which are incompatible with globular shapes; these proteins must therefore have elongated or fibrous structures within the ribosome. On the other hand, only two proteins of the 50S subunit, namely L11 and L18, have so far revealed two separated antibody binding sites; proteins L7/L12 occurred, however, at multiple sites.