Structure and function of Escherichia coli ribosomes : II. Translational fidelity and efficiency in protein synthesis of a protein-deficient subribosomal particle

Abstract

Treatment of 30 s subribosomal particles with cesium chloride yields 23 s core particles and a split protein fraction (SP30) which can be separated into basic and acidic components (SP30A, SP30B) respectively by DEAE cellulose chromatography. Reattachment of SP30B proteins to 23 s core particles yields [23, B] particles which are partially active in polypeptide synthesis, and whose activity is stimulated by SP30A proteins. Further studies described in this paper have shown the following results. (a) The [23, B] particles are partially active in polypeptide synthesis directed by natural mRNA, RNA from phage f2. (b) The [23, B] particles are partially active in the binding of formylmethionyl-tRNA directed by the triplet AUG, random poly AUG or phage f2 RNA. (c) The specific tRNA binding experiments done either with poly U-Phe-tRNA or f2 RNA-fMet-tRNA systems indicate that the stimulation by SP30A proteins is due to an increase in the number of specific binding sites, hence probably the number of active particles, in the preparation. (d) Possible increase in translation error was examined in the system with the [23, B] particles and the native 50 s particles using poly U or the poly (U-U-C) with the repeating sequence as an mRNA. No significant increase was observed compared to the system with the native 30 s particles. Thus, the deletion of the SP30A proteins from the 30 s particle does not change the translational fidelity of the particle. It is suggested that [23, B] particles can assume several different structures, some active and others inactive, and that, in the presence of the SP30A proteins, only the active form of the [23, B] particle is structurally permitted in [23, A,B] particles.