Plasmid DNA isolation by the cleared lysate method

The cleared lysate method of plasmid isolation is commonly used to extract relatively small plasmids (up to about 20 kb) from gram-negative bacteria such as Escherichia coll. It relies on a very gentle lysis of the bacteria to release small molecules, including very compact, supercoiled plasmid, into solution, while trapping larger molecules, such as chromosomal DNA fragments, in the remains of the cells. A high-speed centrifugation pellets cell debris and trapped chromosomal DNA, to produce a 'cleared lysate' highly enriched for plasmid.