Rotating gels: Why, how, and what

Gel electrophoresis performed by use of an electrical field that varies temporally in either magnitude or direction (pulsed-field gel electrophoresis, or PFGE) has been used to (a) improve the fractionation by length of linear, double-stranded DNA and (b) prevent arrest of particles that become sterically trapped in the network of fibers in a gel; these particles include open circular DNA and DNA-protein complexes. The procedure initially developed for pulsing the electrical field was varying the electrical potential on electrodes. Alternatively, pulsing can be achieved by rotating the gel. The following advantages were originally achieved by using rotation of the gel: simplified apparatus, unrestricted field-gel angle, more uniform pH and temperature, and accessibility of modes of PFGE that depend on continuous change of the field-gel angle. More recently, advances in equipment have yielded the following: temperature control that is improved (±0.2°C), less expensive, and less space-consuming; electrical potential gradient that is more accurate (±2%); control of rotation that is completely user-programmable; and monitoring of temperature during electrophoresis.