The effect of linker length on tandem hairpin functionality was assayed by EMSA. The assay was performed as described in the legend to Figure 3A. Control reactions were performed in the absence or the presence of E2dbd (lanes 1 and 2, respectively). Competition experiments with tandem polyamides PA5 (lanes 3–10), PA6 (lanes 11–18) and PA1 (lanes 19–26) are shown. Netropsin, a natural product containing two pyrroles, is used as a reference standard in this experiment (lanes 27–34). Polyamide concentrations surveyed were 0.13 (lanes 3, 11, 19 and 27), 0.64 (lanes 4, 12, 20 and 28), 3.2 (lanes 5, 13, 21 and 29), 16 (lanes 6, 14, 22 and 30), 80 (lanes 7, 15, 23 and 31) and 400 nM (lanes 8, 16, 24 and 32) and 2 (lanes 9, 17, 25 and 33) and 10 µM (lanes 10, 18, 26 and 34).