Escherichia coli Elongation Factor G is inhibited ireversibly by the chemical modification of 1 cysteine residue with N-ethylmaleimide. At pH 5.2, this cysteine is approximately 130 times more reactive than beta-mercaptoethanol toward N-ethylmaleimide. Inhibition is not prevented by either the ribosome or GTP alone at concentrations approximately equal to that of Elongation Factor G, but in com...