A COMPUTER-SIMULATION ACCOUNTING FOR DISSIMILAR ELECTROPHORETIC BEHAVIOR BETWEEN 2 SIMILARLY CURVED DNA FRAGMENTS DUE TO A DIFFERENCE IN ARC-LENGTH

Arc-shaped bent DNA fragments of the same predicted planar curvature but differing in length by 20% were compared in regard to their mobilities in 3 to 10% polyacrylamide. The longer (155 bp) fragment is retarded far more severely than the shorter (124 bp) fragment. The effect of gel concentration in promoting the retardation is far more pronounced for the 155 bp than for the 124 bp fragment. Moreover, a temperature change from 25 degrees C to 4 degrees C does not substantially affect the gel concentration dependent mobility of the 124 bp fragment while it increases the retardation of the 155 bp fragment greatly. The strong increase in retardation brought about by a mere 20% increase in the length of the are was accounted for by a simple computer simulation of gel electrophoresis which considered the rate of passage of are-shaped objects through a two-dimensional array of disc-shaped obstacles. Since the simulation relies exclusively on geometric factors, its success in predicting the behavior of the 124 and 155 bp DNA fragments suggests that geometric factors are largely responsible for their electrophoretic properties. The simulation can account for the strong temperature effect on the retardation of a model of the 155 bp DNA in polyacrylamide gels by showing that a decreased degree of random motion has a profound effect on the modeled 155 bp particle, but not on the modeled 124 bp DNA.