l,lO-Phenanthroline-Copper Ion Nuclease Footprinting of DNA-Protein Complexes in Situ Following Mobility-Shift Electrophoresis Assays

The existence of cell-type specific promoter and enhancer elements has been known for several years. However, the mechanisms responsible for the remarkable specificity of such elements, in comparison to the ubiquitously active promoters and enhancers of “house-keep ing” genes and DNA tumor viruses, have remained elusive until recently. Although transfection and mutagenesis experiments have taught us a great deal about the structure of cell type-specific &-acting elements, the breakthrough in understanding the molecular basis for the differential activity of these elements has come from the analysis of their recognition by specific DNA-binding proteins.