Figure 1.
Secondary (a) and tertiary (b) structures of transfer RNA (tRNA). The cloverleaf secondary structure folds to the L-shaped tertiary structure; both structures have corresponding colors. tRNA has the universal single-stranded CCA-3′ terminus and a neighboring nucleotide at position 73 called “discriminator”, which is also non-base-paired in most cases. Several positions are numbered to facilitate the discussion.