Resolving Multimegabase DNA Molecules Using Contour-Clamped Homogeneous Electric Fields (CHEF)

Contour-clamped homogeneous electric field (CHEF) gelelectrophoresis is a particular formulation of pulsed-field gel electrophoresis (PFGE), which uses an array of electrodes positioned around the gel (on a contour) and clamped to specific voltages to produce a nearly homogeneous electric field inside the contour (1 ). The direction of the electric field is changed periodically, as with all pulsed-field techniques. In the case of CHEF, field reorientation is achieved electronically by changing the voltages (potentials) of the various electrodes in the array (see Fig. 1 ). Commercial CHEF devices currently employ a hexagonal electrode array, but other types of contours, such as circles or squares, if properly clamped, can also produce alternating homogeneous electric fields.