FIGURE 6.3 - Diagram of a BioRad CHEF-DR III system. The unit consists of a variable speed pump (normally set to a speed of "70"), a cooling module (usually set between 12°C and 16°C), a programmable control/power unit, and an electrophoresis chamber characterized by a hexagonal array of electrodes. To begin operation, 2.5 L of electrophoresis buffer (e.g., 0.5X TBE) is added to the electrophoresis chamber. The control/power unit and the cooling module are then turned on. Buffer is pumped through the electrophoresis chamber by the variable speed pump. The buffer leaving the chamber is cooled by the cooling module and returned to the electrophoresis chamber. An agarose gel is placed in the electrophoresis chamber as shown. Parameters including initial switch time, final switch time, run time, volts/cm, and included angle are entered using the keypad on the control/power unit. The electrophoresis chamber can be drained by removing the clamp from the drain hose.