Effect of pools of RNA selected for binding to SMD-Ll1 (SELEX E and SELEX F) or to SMD-Ll2 (SELEX G) on the activity of their cognate enzyme. Activity of SMD-Ll1 or SMD-Ll2 in the presence of all pools of RNA obtained from SELEX E (top, Ll1), SELEX F (middle, Ll1) or SELEX G (bottom, Ll2) at SMD:RNA molar ratios of 1:1 was calculated from fluorescence measurements. SMD activity is expressed as percent of the fluorescence counts obtained with each protein in the absence of RNA (black bars). Data shown are averages of three experiments (n = 3), each in triplicate (SELEX E and F) or duplicate (SELEX G), ± standard error of the mean (SEM). Significant differences (P < 0.001), determined by ANOVA of repeated measures and the Tukey post-test, are shown as §, relative to protein alone in the absence of RNA; *, relative to s1; and †, relative to s12.