Protein synthesis catalyzed by thiol blocked ribosome preparations

Ribosome preparations respond heterogeneously to thiol blocking agents such as N-ethylmaleimide. About 55% of the particles rapidly lose the ability to catalyze peptide bond formation. The remaining 45% are immune. The only function related to peptide bond formation that appears abnormal in inactivated ribosomes is messenger RNA-directed transfer RNA binding. The change, however, is small relative to the alteration in activity observed. Thus it appears that thiol blocking, which selectively damages 30 S subunits, renders about half the 30 S subunits unable to co-ordinate properly with 50 S subunits in peptide bond formation. The implications of these results with regard to ribosome heterogeneity are discussed.