[Binding of a fragment of yeast phenylalanyl tRNA containing an anticodon loop with 30S and 70S ribosomes from Escherichia coli. The role of guanosine-42 in this interaction].

Poly(U)-dependent binding of isolated yeast tRNA(Phe) anticodon hairpin (15-nucleotide-long, corresponding to nucleotides 28-42 within the tRNA) and several its derivatives to the P site of Escherichia coli 30S and 70S ribosomes was studied quantitatively. The affinity for the hairpin binding to 70S ribosomes was shown to be only 30-fold weaker than that for the binding of total tRNA(Phe). Within the anticodon hairpin, removal of the 3'-terminal nucleotide corresponding to guanosine-42 in tRNA(Phe) decreases the association constant for the anticodon arm-ribosome interaction 15-fold. Replacement of this guanosine with other nucleosides does not affect the affinity, regardless of involvement in the hairpin secondary structure. These data indicate that G-42 affects the anticodon arm affinity most likely by forming a direct contact with the ribosome. One can assume that this nucleotide within intact tRNA also forms a contact with the P site. Since the 3'-terminal ribose modifications (oxidation, oxidation and reduction) as well as the presence or absence of the 3'-terminal phosphate does not affect the affinity of the anticodon arm fragment, the latter is obviously involved in the interaction through 3'-terminal nucleotide base groups which does not take part in base pairing.