DNA extraction from fresh or frozen tissues

The first step in molecular analysis of patient tissues is preparation of purified, high molecular weight DNA. A number of methods and commercial kits are available for DNA isolation. Traditional organic extraction protocols (1,2) are based on the fact that DNA is soluble in water whereas lipids are soluble in phenol. In these protocols, tissues are disaggregated and then treated with detergent to lyse cell membranes followed by proteinase to digest proteins. Phenol, an organic solvent, is added to help separate the lipids and protein remnants from the DNA. Chloroform is then used to facilitate the removal of phenol. DNA is subsequently concentrated and further purified by precipitation in a cold mixture of salt and ethanol. Finally, DNA is resolubilized in Tris-EDTA buffer.