Controlling electrophoretic trapping of circular DNA by addition of starchpreparations to agarose gels

Starch preparations were added to agarose gels to enhance the electrophoret ic trapping of circular plasmid DNA. The critical voltages required to trap the open circular (OC) and the supercoiled (SC) forms of a 13.1-kbp plasmi d were measured in gels composed of agarose and added starch preparations. Modified starch preparations reduced the critical voltage required to trap the OC form of the plasmid to approximately one-third of the control value (in 1% agarose gels). Amylose (a fraction of starch with a low amount of br anching) also reduced the critical voltage to trap the OC form in a similar manner. The critical voltage to trap the SC form of the plasmid was not si gnificantly reduced by the starch preparations. The capacity to trap OC DNA was increased by the addition of higher amounts of the starch preparations added to the gels. Field inversion gel electrophoresis was used to charact erize the length of the traps in the gels. The starch preparations and amyl ose increased the trap lengths approximately twofold. The increased trap le ngth correlated with the decreased critical voltage required to trap the OC form of the 13.1-kbp plasmid.