Gel Shift, or Band Shift Assay, or Electrophoretic Mobility Shift Assay (EMSA) is a technique for studying gene regulation and determining protein:DNA interactions. The assay is based on the observation that complexes of protein and DNA migrate through a non-denaturing polyacrylamide gel more slowly than free DNA fragments or double-stranded oligonucleotides. The gel shift assay is carried out by first incubating a protein(s) (such as nuclear or cell extract) with a 32P end-labeled DNA fragment containing the putative protein binding site. The reaction products are then analyzed on a nondenaturing polyacrylamide gel. The specificity of the DNA-binding protein for the putative binding site is established by competition experiments using DNA fragments or oligonucleotides containing a binding site for the protein of interest or other unrelated DNA sequences.

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