Studies on T. Utilis tRNA^TYr variants with enzymatically altered D-loop sequences. II. relationship between the tertiary structure and tyrosine acceptance

The nucleotide sequence of T. utilis tRNA^TYr has been modified to have a deletion or substitution of the "conserved" nucleotide sequence Gm¹⁸-G¹⁹ in the D-loop by enzymatic procedures in vitro. Conformations of the variant tRNAs were analyzed by measuring melting profiles and electrophoretic mobiities in "native" polyacrylamide gels, and by examining the RNase T₁ digestion patterns in sequencing gels. The results obtained shed light on the importance of the interaction between the sequence Gm¹⁸-G¹⁹ and nucleotides in the TPSgr;C-loop (probably PSgr;57-C⁵⁹ for the maintenance of the total conformation of tRNA^TYr in solution. The association of D-loop and TΨC-loop regions in the variant tRNA^Tyrs is slightly relaxed even at room temperature and melting occurred at temperatures higher than 40°C. The relationship between the tertiary structure of the variant tRNA and its aminoacylation capacity was assayed at various temperatures. The results indicate that highly ordered tertiary structure is needed for tRNA^Tyr to be fully aminoacylated.