Rapid purification of plasmid DNAs by hydroxyapatite chromatography [yeast extract, Escherichia coli strains and plasmids]

A method is described for the rapid preparation of plasmid DNAs of molecular weight up to 14 × 106. This method involves the chromatography, at room temperature, of bacterial cleared lysates on hydroxyapatite in the presence of high concentrations of phosphate and urea. All detectable protein and RNA contamination of plasmid DNA is removed by this procedure and the conformation of the plasmid DNA is unaffected. Less than 0.5% chromosomal DNA is present in the purified preparation and even this can be removed if necessary by a simple extention of the procedure to include a heat‐denaturation step. The method is extremely rapid and amenable to large‐scale plasmid preparation; 5 mg ColE1 DNA have been purified within 40 min. The yield of plasmid DNA is similar to that obtained with the conventional dye‐centrifugation technique, however the purity is greater.