Structure of LiCl core particles of 50 S ribosomal subunits from Escherichia coli by electron microscopy.

The structure of 50 S E. coli ribosomal subunits was studied by electron microscopy as these particles were gradually depleted of proteins by incubation with 0.5 to 6.0 m LiCl. Changes observed in the structure of the depleted subunits were correlated with the location of the deleted ribosomal proteins on the control 50 S particle. These changes were particularly striking in the "crown" region, the site of a considerable number of the proteins necessary for the biological activity of the 50 S subunit. Protein L 16, the first to be removed by the LiCl treatment, was found to be essential for the structural integrity of the large subunit through interactions with ribosomal proteins residing in the left-hand side crest and the interface. Based on electron microscopic evidence, a scheme was proposed for the structural changes accompanying the stepwise unfolding of the 50 S E. coli subunit by LiCl.