Fluorescence melting curves for the oligonucleotides in the presence of 10 mM lithium phosphate pH 7.4 containing different concentrations of KCl. The samples were heated and cooled at 0.2°C min–1. In each case the potassium concentration increases from left to right; 0, 1, 2 and 5 mM KCl for GGG-Oct and GGG-H1 and 0, 1, 2, 5, 10 and 40 mM KCl for GGG-Prop, GGG-H2 and GGG-TTA. The bottom right hand panel compares the melting and annealing curves for GGG-H2 in the presence of 10 mM lithium phosphate, containing 1 mM KCl. In each case the solid lines show van’t Hoff fits to the data points as described in the Materials and Methods section.