BINDING OF THE ANTICODON LOOP OF YEAST TRNA(PHE) TO ESCHERICHIA-COLI 30S RIBOSOMES - ROLE OF G42

A quantitative study was made of poly(U)-dependent binding of the isolated yeast tRNA(Phe) anticodon loop (nucleotides 28-42) to the P site of the E. coli 70S ribosome and 30S subunit. The affinity of the isolated loop to the P site was only 30 times lower than that for tRNA(Phe). Removal of the 3'-terminal nucleotide corresponding to G42 in tRNA(Phe) reduced the affinity of the loop to the P site by a factor of 15. Its replacement by other nucleotides including the one complementary to the 5'-terminal residue, as well as removal of the latter, had no effect on the affinity. These data indicate that the 3'-terminal nucleotide of the loop and, consequently, the corresponding residue of tRNA (G42) directly contact the P site. Modification of the 3'-terminal nucleotide and attachment of a phosphate group to the 3' terminus had no effect on the affinity, suggesting that interaction with the ribosome involves only the nucleic base.