The purpose of this step is to disrupt the ionic interactions between positively charged histones and the negatively charged backbone of DNA. This step is achieved by using an anionic detergent such as sodium dodecyl sulphate (SDS) to bind to the proteins and give them extensive anionic character. A secondary action of SDS is to denature DNases and other proteins. Optionally, a broad spectrum proteolytic enzyme such as proteinase K can be used to digest histones and further inactivate DNases. Alkaline pH and high concentration of salts improve efficiency of this step.