Gel electrophoresis measurement of counterion condensation on DNA

Abstract

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) , and sperinidine³⁺, 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 predict ions from counterion condensation theory for two‐counterion mixtures. © 1995 John Wiley & Sons, Inc.