Chicken liver ribosomes: Characterization of cross-reaction and inhibition of some functions by antibodies prepared against Escherichia coli ribosomal proteins L7 and L12

Antibodies prepared in rabbits against Escherichia coli ribosomal proteins L7/L12 are reported to be immunologically cross-reactive with some ribosomal proteins on the 60 S subunit of eukaryote ribosomes (Wool & Stöffler, 1974; Stöffler et al., 1974). We have confirmed these reports and extended this finding to a detailed study of the functional properties of eukaryote ribosomes which are affected by these cross-reacting antibodies. We report here the partial reactions in protein synthesis that are inhibited by the anti-L7/L12 IgG (immunoglobulin G) preparations using a chicken liver system. The following reactions were inhibited: EF-1 (elongation factor 1) dependent binding of aminoacyl-tRNA to ribosomes and GTP hydrolysis; EF-2 dependent binding of nucleotide to ribosomes and GTP hydrolysis; binding of ¹⁴C]ADP-ribosyl · EF-2 to ribosomes. This last reaction is more sensitive to the antibody inhibition than the corresponding nucleotide binding reaction. We show that the inhibitions were not simply non-specific precipitation of ribosomes by IgG, in that monovalent Fabs were also inhibitory, and peptidyl transferase activity was not inhibited. The functions inhibited with the IgG preparations in the chicken liver system are analogous to those inhibited in the homologous E. coli system. Thus the cross-reacting protein is functionally as well as immunologically conserved.