The Gel Retardation Assay

The gel retardation or electrophoretic mobility shift assay (EMS A) is a sensitive technique for studying protein–DNA interactions. Originally devised by Fried and Crothers (1 ) to study the kinetics of protein‐DNA interactions, the method relies on the stability of protein DNA complexes when subject to nondenaturing polyacrylamide gel electrophoresis. The DNA is radiolabeled to enable rapid detection and in its native state it migrates quickly through the gel matrix. Protein binding generates slower mobility protein‐DNA complexes that resolve as discrete bands.