Details are described here for using a rotating gel to perform pulsed field agarose gel electrophoresis (PFGE) with programmable control of the following variables: magnitude of the electrical field, polarity of the electrical field, temperature of the gel and position of the rotating disk upon which the agarose gel rests. By use of this procedure for programmable control, modes of PFGE have been explored that have the following characteristics: (i) resolution by DNA length is completely lost for DNA shorter than a critical length that increases as the pulse times increase, and (ii) resolution by DNA length is enhanced for longer DNAs that are shorter than a second critical length. This window of resolution can be moved to the position of the 2-6 Mb chromosomes of Schizosaccharomyces pombe.
An autotransformer was preferred for the heater, as a transformer does not heat up as readily as a rheostat and, thus, provides a more constant volt-amperage supply to the heater.An exploded view of the heater (rated at 110 watts and 115 volts, in Figure 2 shows how it may be disassembled for replacement of burned out heating units (available from American Instrument Co., Silver Spring, Md., as replacement parts of an electric micro-Kjeldahl digestion apparatus). When assembled, the small plate (containing side vents for air cooling) which has the heater attached to it, fits into the box and the lid fits tightly over the top.The details of the heater construction are shown in scale drawings in Figure 3. This box and support plate are made of Transite. The heater unit, A, is fastened to the support plate beneath it with four small spacing nuts. A similar set of spacing nuts fastens the electrical contacts to the unit: the nuts are easily removed to replace a heater unit. As the heating unit never becomes extremely hot during an analysis, ordinary coated wire was found to be satisfactory for lead wire from the heater to the power control.
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