title: Rapid purification of plasmid DNA by a single centrifugation in a two-step cesium chloride-ethidium bromide gradient.
abstract: A procedure for rapid, preparative purification of plasmid DNA is described and compared with a conventional equilibrium centrifugation method. A discontinuous, two-step CsCl-ethidium bromide gradient is used, with the starting position of the plasmid-containing extract being at the bottom of the tube. During centrifugation in a fixed angle rotor, covalently closed circular plasmid DNA is separated from contaminating protein, RNA, and chromosomal DNA in 5 hr. Plasmids purified by this method are considerably less contaminated with RNA than when purified by a 48-hr equilibrium run in a homogeneous gradient, as determined by agarose gel electrophoresis and 5'-end-labeling studies. Plasmid DNA purified in two-step gradients can be used directly for restriction endonuclease analysis and DNA sequencing.
mesh_terms: D001345:Autoradiography; D002499:Centrifugation, Density Gradient; D002586:Cesium; D004269:DNA, Bacterial / Q000302:isolation & purification*; D003720:Densitometry; D004587:Electrophoresis, Agar Gel; D004926:Escherichia coli / Q000378:metabolism; D004996:Ethidium; D010957:Plasmids; D013194:Staining and Labeling
chemical_list: D004269:DNA, Bacterial; D002586:Cesium; D004996:Ethidium