The gel shift, or electrophoretic mobility shift, assay provides a simple and rapid method for detecting DNA-binding proteins. Promega has developed the Gel Shift Assay System, which contains target oligonucleotides, a control extract containing DNA-binding proteins, binding buffer and reagents for phosphorylating oligonucleotides. The Gel Shift Assay Core System includes sufficient HeLa nuclear extract to perform 20 control reactions, Gel Shift Binding 5X Buffer, an SP1 Consensus Oligo and an AP2 Consensus Oligo. This is a reliable system for obtaining experience with gel shift assays because AP2 binding activity is stable and produces a strong gel shift.