Initially, we have attempted to crystallize RNA-inhibitor complexes in the same crystal form whose structure we have solved, in order to solve the new structures by isomorphous difference methods. Unfortunately, we have found that only one of the new inhibitor strands crystallizes in the same form (the all-DNA strand with a dG at the cleavage site), and those crystals do not diffract. Thus, it appears that, although the nucleotides around the cleavage site do not make any intermolecular contacts, changes in these nucleotides perturb the overall conformations of the ribozyme sufficiently to deter formation of well-ordered crystals. Therefore, we have searched for new crystal forms.