Control of pH during plasmid preparation by alkaline lysis of Escherichia coli.

Alkaline lysis of Escherichia coli is usually the method of choice for plasmid preparation, but ''ghost bands" of denatured supercoiled DNA can result if the pH is too high or the period of lysis is too long. By replacing the usual sodium hydroxide lysis solution with an arginine buffer prepared in the range of pH 11.4 to 12.0, we were able to stabilize the pH during lysis and obtain plasmid that is suitably pure for restriction digestion and DNA sequencing.