The oligoribonucleotide analogs of the invention, as exemplified in the figure, are relatively small, three-dimensional structures derived from larger parental RNA molecules. The analogs include a first nucleic acid structure including one or more nucleotide sequences that are derived from a region of parental RNA, wherein in its native state, the region binds to a ligand, e.g., an aminoglycoside, with a parental RNA ligand binding pattern, and a second nucleic acid structure including one or more nucleotide sequences combined with the first nucleic acid structure to form the analog and provide the analog with a conformation that binds the ligand with a ligand binding pattern that is substantially identical to the parental RNA ligand binding pattern. These analogs can be used to identify novel therapeutic compounds.