Purification of DNA binding proteins by affinity and ion exchange chromatography

It is the exquisite interplay of proteins and nucleic acids within the cell which gives rise to the controlled expression and replication of the genetic material. Our present understanding of these processes is in part the result of the successful purification and characterization of the participating macromolecules. The achievements of the early molecular biologists in obtaining active, homogeneous preparations of low-abundance gene regulatory proteins are outstanding. The strategies employed for the purification of such proteins are, however, no different in principle to those procedures used to purify high-abundance proteins. Moreover, one of the goals of molecular biologists in purifying gene regulatory proteins is to clone the corresponding gene. When this has been achieved, the gene can often be overexpressed, and the purification of the gene product becomes trivial by comparison.