Comments
Dextran sulfate is a heparin-like polysaccharide, which improves the hybridisation rate of nucleic acids, depending on the probe employed, by a factor of 3 - 100 (2-4). This results from a reduction of the volume of the DNA-containing sample by the polymere, leading to a DNA-concentration (1, 4). Dextran sulfate should only be applied, when the hybridisation rate or the DNA-quantity is a limiting factor for the identification of 'rare' sequences. The highest effect with Dextran sulfate is observed with polynucleotides of > 250 nucleotides in length. There is no improvement with oligonucleotides less than 14 bases in length. In addition, there is no advantage for the hybridisation of bacterial colonies or plaques. It even may result in a high back ground. The handling of Dextran sulfate is made more difficult by its high viscosity (4).A 50 % stock solution is slightly yellow (2), the working concentration is 10 %. If aqueous solutions of Dextran sulfate have to be autoclaved, they have to be buffered with sodium bicarbonate to prevent a decomposition during autoclaving.
Literature
(1) Wetmur, J.G. (1975) Biopolymers 14, 2517-2524Acceleration of DNA renaturation rates. (2) Wahl, G.M. et al. (1979) Proc. Natl. Acad. Sci. USA 76, 3683-3687. Efficient transfer of large DNA fragments from agarose gels to diazobenzyloxymethyl-paper and rapid hybridization by using dextran sulfate. (3) Meinkoth, J. & Wahl, G. (1984) Anal. Biochem. 138, 267-284. Review: Hybridisation of immobilized nucleic acids. (4) Sambrook, J., Fritsch, E.F. & Maniatis, T. (1989) Molecular Cloning: A Laboratory Manual. 2nd Edition page 9.50. Cold Spring Harbor Laboratory Press. Cold Spring Harbor, New York.
