Figure 2.

The cloverleaf hammerhead construct used in these experiments and its ribozyme activity. The cloverleaf hammerhead species is made from a single strand, forming helix III of 10 bp, and helices I and II, each of which comprise 4 bp closed by a tetraloop. DNA residues are shown open, and RNA residues are shown in bold letters. For ease of synthesis, ribouridine replaced thymine in the otherwise-DNA sections, leading to two rU-dA base pairs. The numbering system follows Hertel et al. (39). Positions U4 and U7 were substituted by 2′-O-methyl-5-FU, the structure of which is shown (Left Inset). (Right Inset) The result of cleavage reactions of ribo-C17-containing FU-substituted hammerhead ribozymes, carried out at 37°C in the presence of 10 mM Mg²⁺.