Specificity of Elongation Factor Tu from Escherichia coli with Respect to Attachment of the Amino Acid to the 2' or 3'-Hydroxyl Group of the Terminal Adenosine of tRNA

Abstract

Modified Tyr‐tRNA^Tyr and Phe‐tRNA^phe species from yeast having the aminoacyl residue bound specifically to the 2′ and 3′ position of the terminal adenosine, respectively, were investigated for their ability to form ternary complexes with Escherichia coli elongation factor Tu and GTP. Both Tyr‐tRNA^Tyr‐CpCpA(2′d) and Tyr‐tRNA^Tyr‐CpCpA(3′d) derivatives which are esterified with the amino acid on the 3′ and 2′ position respectively and which lack the vicinal hydroxyl were able to form ternary complexes. The stability of these ternary complexes was lower than in the case of native Tyr‐tRNA^Tyr‐CpCpA. Tyr‐tRNA^Tyr‐CpCpA(3′d) having the amino acid attached to the 2′ position interacted considerably more strongly with EF‐Tu. GTP than Tyr‐tRNA^Tyr‐CpCpA(2′d). Ternary complex formation was observed with neither Phe‐tRNA^phe‐CpCpA(2′NH₂) nor Phe‐tRNA^Phe‐CpCpA(3′NH₂). It is concluded that 2′ as well as 3′ isomers of native aminoacyl‐tRNA can be utilized for ternary complex formation but in a following step a uniform 2′‐aminoacyl‐tRNA. EF‐Tu. GTP complex is formed. Although the free vicinal hydroxyl group of the terminal adenosine is not absolutely required, replacement of the ester linkage through which the amino acid is attached to tRNA by an amide linkage leads to loss of ability to interact with elongation factor Tu.