Studies on T. utilis tRNA^Tyr Variants with Enzymatically Altered D-Loop Sequences. I. Deletion of the Conserved Sequence Gm-G and Its Effects on Aminoacylation and Conformation

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Variants of T. utilis tRNA^TYr containing deletions or substitutions of nucleotides in the D-loop region have been prepared by several enzymatic reaction steps in vitro. Although these variants lack the “conserved” nucleotides Gm¹⁸-G¹⁹ in their D-loop, their tyrosine-accepting capacities are indistinguishable from that of the native tRNA^Tyr. Thermal denaturation studies with tRNA^TYr variants lacking the Gm¹⁸-G¹⁹ sequence have revealed a biphasic nature of the melting profile, suggesting the loss of tertiary interactions between Gm¹⁸-G¹⁹ and somewhere in the molecule (probably in the TΨC-loop region). These results indicate that nucleotide sequences around Gm¹⁸-G¹⁹ (i.e. D¹⁶-D-Gm-G¹⁹ or Gm¹⁸-G-D-D-²¹) themselves are not essential sites for the recognition of tRNA^TYr by T. utilis tyrosyl-tRNA synthetase and that tRNA^TYr variants with an apparently “relaxed” conformation still have full aminoacylation capacities at around 30°C.