CD spectra are plotted as ellipticity (millidegrees) versus wavelength. Smooth curves represent the average of three separated scans at 1 nm sampling interval from 210 to 350 nm. (A) CD spectra of L-RNA target in complex with D-RNA (hammerhead ribozyme). (B) D-RNA target with L-RNA (hammerhead ribozyme). (C) control experiment with the use of D-RNA (5′GGCGACCGACUGU3′) not fully complementary to L-RNA (hammerhead ribozyme). There are differences in the Cotton effect of the complexes. Black squares correspond to D- or L-RNA (ribozyme), (33-mer); black circles refer to L- or D-RNA target (14-mer), open squares represent mathematical sum of CD spectra of hammerhead ribozyme and RNA target, open circles correspond to a mixture of D-or L-hammerhead ribozyme with D-or L-RNA target without incubation step. Black stars show a complex of D- or L-RNA (ribozyme) with D- or L-RNA target preincubated at 90°C and slowly renatured overnight.