Figure 1.

Sequence and cloverleaf structure of tRNA^Cys of E. coli, yeast (S. cerevisiae), and human. The U73 nucleotide, the GCA anticodon, and the G15⋅G48 tertiary base pair, which are important for aminoacylation of the E. coli tRNA by the E. coli enzyme, are highlighted by shaded circles. U73 and GCA are conserved in evolution and are important for aminoacylation of the yeast and human tRNAs by the respective homologous enzymes. In contrast, both the yeast and human tRNAs have G15⋅C48 (open circles) but do not specifically require this base pair for aminoacylation.