A simple single-step procedure for small-scale preparation of Escherichia coli plasmids.

Numerous rapid procedures to prepare relatively pure plasmid DNA from small volumes of E. coli cultures have been developed for restriction mapping purposes [ 1-4] . Some of these procedures demand lengthy fractionation steps involving lysozyme-mediated cell lysis, boiling, phenol/chloroform extractions and DNA precipitations. Here we describe a procedure which allows isolation of plasmid DNA on a mini-scale, demanding no more than 20 minutes. The principle is based on the finding that phenol/chloroform treatment of E. coli cells in the presence of LiCl and Triton X-100 solubilises the plasmid DNA, concomitantly precipitating the unwanted denatured chromosomal DNA and the cellular proteins. The procedure is as follows: