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

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-D²¹) 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.