C.Lang & M. Lang, April 2004
Pulse Field Gel Electrophoresis (PFGE) is a method for size separation
of large DNA fragments for BAC cloning and many other purposes.
Different electrophoresis systems are available, for example FIGE (Field
Inversion Gel Electrophoresis) (1) (2) or CHEF (Clamped Homogeneous
Electric Fields) (3). These methods are based on rhythmic and
symmetrical oscillation of the electric field direction during gel
electrophoresis. The electric field oscillates around a certain axes at
a certain angle, usually 90°-120° (oscillation must occur
regarding switch angle and switch time). Over time, the field vectors
result in a single "main field direction". Some electrophoresis systems
are able to freely re-orientate this main axis by a free determination
of the extreme angles. However, not all commercially available CHEF
systems have this option.
BAC cloning (6) sometimes requires a back and forth migration of DNA
fragments inside the agarose gel (7). Here we describe a simple machine
that alternatively switches the electrical connections of oppositely
located electrodes of the gel tank and the CHEF power module. This
results in a complete field inversion of the main electric field
direction without altering any other electrophoresis conditions which
are controlled by the CHEF power module. The principle of this apparatus
was described previously (1). The machine was designed for a 24
electrode CHEF PFGE system (5). It enables both-, a manual and a timer
dependent programmed switch.