Field-inversion gel electrophoresis.

Among the techniques to separate large DNA fragments, field-inversion gel electrophoresis (FIGE, 1)is probably the easiest to perform with a minimum of special equipment. Indeed, the only requirement besides a regular gel electrophoresis box and a power supply is a device enabling the periodic inversion of the electric field direction over the course of the experiment. This method was derived from experiments done on a modified orthogonal-field-alternation gel electrophoresis (OFAGE) apparatus (2) based on the observation that obtuse angles lead to a better separation. The widest angle being 180°, the four electrode pulsed-field gel electrophoresis (PFGE) system was reduced to a standard submarine gel electrophoresis box with only two electrodes. This simple configuration generates a highly uniform electric field across the gel, making the lane to lane comparison very easy (Fig. 1). Two basic electrophoretic modes can be used in order to achieve a net migration in this configuration: