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 70S ribosomes. In perfect agreement with the X-ray structure of the Thermus thermophilus 30S 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.