Electrophoretic mobility-shift assays

Abstract

In an electrophoretic mobility-shift assay (EMSA, or simply "gel shift"), a (32)P-labeled DNA fragment containing a specific DNA site is incubated with a cognate DNA-binding protein. The protein-DNA complexes are separated from free (unbound) DNA by electrophoresis through a nondenaturing polyacrylamide gel. The protein retards the mobility of the DNA fragments to which it binds. Thus, the free DNA will migrate faster than the DNA-protein complex. An image of the gel is used to reveal the positions of the free and bound radiolabeled DNAs.