Figure 1.

The diversity of RNA oligonucleotide substrates for aminoacylation. (Top) The tRNA cloverleaf secondary structure (Left) that folds into an L-shape (Right). The minihelix domain is shaded in red, and the second domain containing the template reading head is shown in blue. (Middle) The variety of oligonucleotide substrates for aminoacylation. All substrates terminate at the 3′-end in the single-stranded NCCA tetra nucleotide, where the identity of N depends on the specific aminoacylation system. The four nucleotides (N₄) of the loop of the tetraloop structure are specifically chosen to impart stability to the short (4 bp) helix joined to that loop (37). (Bottom) The pseudo-knotted RNA circle described by Felden and Giegé (9).