The signal is substantially diminished in the absence of the enhancer. A rigid hydroxyprolinol linker ( Figure 3B ) between the oligonucleotide and fluorophore FL1, critical for sensitivity and specificity, was used in this experiment. The results in Figure 2 illustrate the importance of all components used in the assay. The cleavage of the fluorophore is highly target dependent and its rate is amplified in the presence of the enhancer oligonucleotide. Very low non-target-dependent cleavage is an important feature of the Endo IV assay.