THE MOBILITY MINIMA IN PULSED-FIELD CAPILLARY ELECTROPHORESIS OF LARGE DNA

Pulsed-field capillary electrophoresis represents a new tool for rapid and highly efficient separations of large biopolymers. The method has been utilized here to study dependencies of the electrophoretic mobil ity upon the frequency and pulse shape of applied voltage for large, d ouble-stranded DNA molecules (5-100 kb) migrating in neutral polymer s olutions. Two different shapes of alternating electric field (sine- an d square-wave impulses) were examined with the frequency values rangin g from 1 to 30 Hz. The linear dependence between duration of the forwa rd pulse (at which the DNA molecule experiences a minimum mobility) an d the product N.ln(N) (where N is the number of base pairs) was experi enced in field-inversion gel electrophoresis, while exponential depend ence was found with the sinusoidal electric field. The mobility minima were lower in field-inversion electrophoresis than with the biased si nusoidal-field technique, The DNA (5 kb concatamers) was adequately se parated using a ramp of frequency in the square-wave electric field, i n similar to 1 h. The migration order of DNA fragments was referenced through adding a monodisperse DNA (48.5 kb) into the sample, The band inversion phenomena were not observed under any experimental condition s used in this work.