An improved and rapid procedure for isolating RNA-free Escherichia coli plasmid DNA.

We describe a simple, rapid, and inexpensive procedure for the isolation of plasmid DNA in high yields from Escherichia coli cultures. The procedure entails two main steps, which involve treating intact bacterial cells with phenol/chloroform in the presence of Triton X-100 and LiCl followed by polyethylene glycol precipitation. Plasmid DNA preparations isolated by this method are highly pure and virtually devoid of RNA. The DNA is suitable substrate for restriction mapping, DNA-modifying enzymes, and in vitro transcription with SP6 and T7 RNA polymerases.