Figure 8.

Return gel electrophoresis. (A) The first electrophoresis is a conventional PAGE with high-salt conditions (89 mM Tris, 89 mM boric acid, pH 8.3) and low temperature (20 °C). If the dye xylene cyanol (XC), present in the samples, is nearly running out of the gel matrix, the buffer is exchanged to low-salt conditions (10 mM Tris, 10 mM boric acid, pH 8.3, 8 M urea), the temperature is raised to 60°C and the direction of the electric field is inverted. (B) During the second electrophoresis step all nucleic acids are denatured; then the circular viroid migrates more slowly than all other, larger nucleic acids. Modified from (102).