Functional interdependence of 50S and 30S ribosomal subunits

Summary

Expression of resistance to erythromycin in Escherichia coli, caused by an altered L4 protein in the 50S ribosomal subunit, can be lost when two additional ribosomal mutations causing resistances to spectinomycin and streptomycin, alterations in the 30S proteins S5 and S12, are introduced into the strain (Saltzman, Brown and Apirion, 1974).

By genetic analysis, using antibiotic sensitive strains as recipient strains in transduction experiments, it was shown that the mutation to erythromycin resistance while unexpressed is kept intact in the genome of such strains. Moreover, using the millipore filter binding assay, it was shown that ribosomes from such strains bind erythromycin to the same extent as ribosomes from the erythromycin sensitive parental strains. This binding can be abolished, i.e. the ribosome may be made resistant again by dissociating the ribosomes to subunits, and the binding can be restored by reassociating the ribosomes.

Thus, an intimate functional relationship between 30S and 50S ribosomal elements was revealed. This interdependence in functional relationships among ribosomal elements depends on the simultaneous alterations in one ribosome of three different proteins, S5, S12 and L4.