Pulsed field electrophoresis in contour-clamped homogeneous electric fields for the resolution of DNA by size or topology.

The electrophoretic separation of DNA molecules can be controlled by the use of contour-clamped homogeneous electric fields (CHEF). This paper describes an improved CHEF apparatus with negligible distortion in the electric fields. When the electric field was periodically reoriented, DNA molecules up to 2 megabases were resolved in a highly uniform manner. Furthermore, when the field strength was changed with orientation, topological variations of conventional-sized DNA molecules were resolved.