REVERSIBLE DISSOCIATION OF ESCHERICHIA COLI RIBOSOMES BY N-ETHYLMALEIMIDE

1. 1. Treatment of extensively washed Escherichia coli ribosomes with N-ethylmaleimide resulted in a reduction of their ability to synthesize polyphenylalanine, bind phenylalanyl-tRNA or form 70-S ribosomes at 8 mM Mg2+. However, at 20 mM Mg2+ reassociation of N-ethylmaleimide-treated ribosomes occurs, and binding of phenylalanyl-tRNA is restored to that of untreated ribosomes. 2. 2. Once reassociated at 20 mM Mg2+ in the presence of polyuridylate and phenylalanyl-tRNA, the N-ethylmaleimide ribosomes can be shifted to 8 mM Mg2+ where they are fully active for dipeptide synthesis and 68% as active for polyphenylalanine synthesis as untreated controls. 3. 3. The N-ethylmaleimide treatment does not preferentially affect the tetracycline or deacylated-tRNA-sensitive binding sites on the ribosome nor does it interfere with enzyme-promoted binding. Consequently, N-ethylmaleimide-reacted sulfhydryl groups may interfere with subunit reassociation but do not prevent ribosome functions associated with peptide-bond formation. © 1969.