Quantitative Analysis of Deoxynucleotide Substitutions in the Codon–Anticodon Helix

The role of 2′ hydroxyl groups in the codon–anticodon helix was evaluated by introducing single deoxynucleotides into each of the six positions in the helix and measuring the affinity of tRNA to either the A site or the P site of Escherichia coli 70 S ribosomes. In perfect agreement with the X-ray structure of the Thermus thermophilus 30 S subunit, A site binding was weaker in five of the six positions but P site binding was unaffected. Since the addition of paromomycin restores A site binding, it appears that the deoxynucleotide substituted complexes are impaired in their ability to promote the ribosomal conformational change that accompanies tRNA binding.