A rapid method for the purification of extrachromosomal DNA from eukaryotic cells

A simple and efficient procedure to purify the low molecular weight extrachromosomal DNA from eukaryotic cells is described. Gentle lysis of cells with urea and sodium dodecyl sulfate in 0.24 M phosphate buffer (pH 6.8) is followed by the removal of high molecular weight bulk DNA by centrifugation. Protein and RNA are removed from the supernatant by hydroxyapatite chromatography in urea/phosphate buffer. Urea is then removed with 0.15 M phosphate buffer and the extrachromosomal DNA, virtually free from protein and RNA, is finally eluted in 0.5 M phosphate buffer. The procedure allows the recovery of about 99% simian virus 40 (SV40) DNA from infected monkey kidney cells in the extrachromosomal fraction. In normal mouse, monkey, andhuman cells, approximately 1% of total cell DNA appears to be extrachromosomal.