POLY(U)-DEPENDENT INTERACTION OF YEAST TRANSFER RNAPHE AND OF ITS FRAGMENTS WITH RIBOSOMES FROM ESCHERICHIA-COLI

We present a quantitative study of the poly(U)-dependent binding of de-acylated yeast tRNA(Phe), of its truncated derivative which lacked the 3-terminal adenosine and of the 15-nucleotide fragment which mimicked the anti-codon hairpin of the yeast tRNA(Phe), with the P-site of the Escherichia coli 70s ribosomes. We measured the equilibrium and rate constants. The 3'-terminal adenosine made a considerable contribution to the free energy of the interaction of the tRNA(Phe) with the P-site of the 70s ribosomes, which amounted to -2.4 kJ/mole at 10 mM Mg2+ and 30-degrees-C. The bulk of the standard free energy change (-45.3 kJ/mole) was due to the binding of the anti-codon hairpin. In addition, the remaining parts of the molecule contributed a further -6.0 kJ/mole in the direct or indirect interaction with the ribosome, altering the conformation of the anti-codon hairpin in a manner which favored binding.