GEL-ELECTROPHORESIS MEASUREMENT OF COUNTERION CONDENSATION ON DNA

We used agarose gel electrophoresis to measure the effective charge neutralization of DNA by counterions of different structure and valence, including Na+, Mg2+, Co(NH3)(6)(3+), and spermidine(3+), which competed for binding with an excess of Tris acetate buffer. Linear DNA molecules ranged in size from 1 to 5 kilobases, and supercoiled plasmid pUC18 was also measured. In all cases, the, results were in good agreement with theoretical predictions from counterion ion condensation theory for two-counterion mixtures. (C) 1995 John Wiley & Sons, Inc.