The Mechanism of Codon-Anticodon Interaction in Ribosomes. Quantitative Study of Codon-Dependent Binding of tRNA to the 30-S Ribosomal Subunits of Escherichia coli

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Abstract
The formation of a ternary complex 30-S-subunit.cntdot.poly(U).cntdot.tRNAPhe is discussed and the conditions for its correct description by Langmuir''s isotherm are deduced. The affinity constant of the binary complex 30-S-subunit.cntdot.poly(U) is measured. The reversibility of binding of tRNAPhe to the complex 30-S-subunit.cntdot.poly(U) is proved in a direct way. The main reason for the heterogeneity of ternary complexes was due to the ability of high MW poly(U) to form complicated aggregates with 30-S subunits. If a fraction of poly(U) of moderate MW (30,000) is used, then the ternary complexes are homogeneous in stability and yield the same affinity constants for deacylated, aminoacylated and peptidyl-tRNAPhe (1 .times. 108 M-1 at 20 mM Mg2+, 200 mM .**GRAPHIC**. and 0.degree. C). Ribosomal protein S1 increases the binding constant of poly(U) with 30-S subunits but does not change the binding constant of tRNAPhe with the 30-S-subunit.cntdot.poly(U) complex. All 30-S subunits, even partially stripped of S1 protein, are active in the binding of both poly(U) and tRNAPhe.