Using capillary electrophoresis to characterize the hydrodynamic and electrostatic properties of DNA in solutions containing various monovalent cations.

This review describes the results obtained by using free-solution capillary electrophoresis to probe the electrostatic and hydrodynamic properties of DNA in solutions containing various monovalent cations. In brief, we found that the mobilities of double-stranded DNAs (dsDNAs) increase with increasing molecular weight before leveling off and becoming constant at molecular weights ≥400 bp. The mobilities of single-stranded DNAs (ssDNAs) go through a maximum at ∼10-20 nucleotides before decreasing and becoming constant for oligomers larger than ∼30-50 bases. The mobilities of both ss- and dsDNAs increase linearly with the logarithm of increasing charge per unit length and decrease linearly with the logarithm of increasing ionic strength. Surprisingly, ss- and dsDNA mobilities level off and become nearly constant at ionic strengths ≥0.6 M. The thermal stabilities of dsDNAs decrease linearly with increasing solution viscosity. The diffusion coefficients of dsDNA are modulated by the diffusion coefficients of their counterions because of electrostatic DNA-cation coupling interactions. Finally, the anomalously slow mobilities observed for A-tract-containing DNAs can be attributed both to differences in shape and to the preferential localization of small cations in the A-tract minor groove. Since many of these results are mirrored in other polyion-counterion systems, free-solution electrophoresis can be viewed as a reporter of the electrostatics and hydrodynamics of highly charged polyions. New results describing the mobilities of dsDNA analogues of a microRNA-messenger RNA complex are also presented.