On the binding of isolated yeast tRNA(Phe) anticodon arm to Escherichia coli 30S and 70S ribosomes. Guanosine-42 is important for the binding.

Conditions for the reversible binding of isolated anticodon arm of yeast tRNA(Phe) (15-nucleotide, corresponding to nucleotides N28-N42) to the P site of Escherichia coli 30S and 70S ribosomes have been determined. The affinity constant for the anticodon arm binding to 70S ribosomes is shown to be only 30-fold weaker than that for the binding of total tRNA(Phe). The affinities of yeast tRNA(Phe) and the anticodon arm for 30S subunits and of the anticodon arm for the total 70S ribosomes are shown to be equal. These data imply that the anticodon arm moiety of tRNA(Phe) mainly contributes to the tRNA-70S ribosome interaction, i.e., it contributes for the most part to the total free energy of the deacylated tRNA(Phe) interaction with the P site of the 70S ribosome. By taking into account additional contacts in the 3'-CCA end, other contacts in the region besides the anticodon arm and 3'-CCA end are presumably absent. Within the anticodon arm removal of the 3'-end nucleotide corresponding to guanosine-42 in tRNA(Phe) decreases the association constant of the anticodon arm-ribosome interaction 15-fold. Replacement of this guanosine with other nucleosides as well as modification of the ribose moiety (oxidation and reduction) does not affect the affinity. The replacement data are very likely to indicate that G42 affects the anticodon arm affinity by forming a direct contact with ribosome.