Primary Purification of Plasmid DNA Using Differential Isopropanol Precipitation

A method for the intermediate recovery of plasmid DNA (pDNA) from alkaline lysates is described that comprises differential isopropanol precipitation steps. In a first low-cut precipitation, a smaller amount of isopropanol (20% v/v) is used so that only high molecular weight RNA precipitates. After solid liquid separation, a high-cut precipitation is performed by bringing isopropanol concentration to 70% v/v to precipitate pDNA. Tests made with lysates show that the differential precipitation increases purity threefold compared to the conventional one-step precipitation at 70% v/v without affecting pDNA recovery (80%).