Invader-mediated recognition of DNA hairpins. (a) illustration of recognition process; (b) sequence and Tm's of DNA hairpins with isosequential (DH1) or non-isosequential (DH2–DH7) stems relative to probes (conditions of thermal denaturation experiments, see Table 1); gel electropherograms illustrating: (c) recognition of DH1 using 200-fold molar excess of five different Invaders, (d) incubation of DH1 with 500-fold excess of unmodified D1:D2 or non-Invader probes Y2:Y6 or Y3:Y5, (e) incubation of DH1 with 200-fold molar excess of single-stranded Y7 or Y9 or Invader Y7:Y9; (f) incubation of DH1–DH7 with 200-fold molar excess of Y7:Y9 (<10% recognition observed with DH5). Conditions: separately pre-annealed probes and targets (34.4 nM) were incubated for ~15h at RT in 50 mM HEPES, 100 mM NaCl, 5 mM MgCl2, 10% sucrose, 1.4 mM spermine tetrahydrochloride, pH 7.2; 12% non-denaturing PAGE run at ~4 °C); DIG: digoxigenin.