Studies on the formation of transfer ribonucleic acid-ribosome complexes. I. The effect of streptomycin and ribosomal dissociation on 14-C-aminoacyl transfer ribonucleic acid binding to ribosomes.

Streptomycin-sensitive 70s ribosomes which are dissociated into SOS and 30s particles by dialysis against 1 X lop4 M magnesium acetate, and then reassociated in 0.02 M magnesium acetate, differ from nondissociated 70s ribosomes in r4C-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. i4C-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 r4C-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 r4C-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.