Studies on the Formation of Transfer Ribonucleic Acid-Ribosome Complexes

Streptomycin-sensitive 70S ribosomes which are dissociated into 50S and 30S particles by dialysis against 1 x 10-4 m magnesium acetate, and then reassociated in 0.02 m magnesium acetate, differ from nondissociated 70S ribosomes in 14C-aminoacyl soluble ribonucleic acid (sRNA) binding. 1. Reassociated ribosomes bind about twice as much 14C-phenylalanyl-sRNA in the presence of polyuridylic acid as nondissociated ribosomes. 2. 14C-Phenylalanyl-sRNA binding to reassociated ribosomes in the presence of polyuridylic acid is reduced 50% by streptomycin; this binding to nondissociated ribosomes is only slightly affected by streptomycin. 3. Streptomycin can inhibit 14C-isoleucyl-sRNA binding to reassociated ribosomes in the presence of polyuridylic acid, but stimulates this binding to nondissociated ribosomes. These effects are greatly influenced by the sRNA-ribosome ratio. Shearing 70S ribosomes by passage through a micropipette also produces Reactions 2 and 3 above, but not Reaction 1. The results indicate that various treatments of the ribosomes (dissociation, shearing) and sRNA to ribosome ratios modify the effects of streptomycin on 14C-aminoacyl-sRNA binding to ribosomes. In addition, the data suggest that different mechanisms may be involved in the effects of streptomycin on inhibiting protein synthesis and on stimulating ambiguous codon recognitions.