FIGURE 4.
Active variant (r4.dom) isolated from the selection. The predicted secondary structure is based on that of the wild-type b1-207t ribozyme. All residues shown in uppercase were doped at a level of 70% during the selection, while those residues shown in lowercase were held constant. Invariant (red) and semi-conserved (blue) residues identified by Ekland and Bartel (1995) are indicated. Residues that differed from those originally found in the parental ribozyme are boxed in grey, with the inverted base pair boxed in yellow. The original sequence identity of each position is indicated in parentheses. The sequences of the 3′ constant region and the substrates PPPS (red line) and SOH (blue line) are given in Materials and Methods.