FIGURE 1.

The hairpin ribozyme. The sequence of the hairpin ribozyme in the cleavage form used in these studies. The ribozyme comprises four strands (a–d). The cleavage site is marked with an arrow, and the locations of G8 and A38 are highlighted in bold. Coaxially stacked arms A and D are shown in black and C and D in gray to be consistent with the folding scheme shown in Figure 4A. The inset shows the local structure of the imidazole nucleotide (shown in its nonprotonated form) incorporated into the “a” strand at position 8.