Protection analysis (or "footprinting") of specific protein-DNA complexes in crude nuclear extracts using methidiumpropyl-EDTA-iron (II).

Endonuclease protection or "footprinting" analysis is a powerful technique for identifying the nucleotides involved in a protein-DNA interaction. DNase I is the most often employed endonucleolytic agent; however, this endonuclease does not exhibit the true nonsequence-specific cleavage desired for this type of analysis. Methidiumpropyl-EDTA (MPE) is a synthetic DNA intercalator that cleaves DNA in the presence of ferrous ion and oxygen. Cleavage by MPE exhibits no sequence specificity, a characteristic that makes this reagent better suited for protection analysis. Here we report a generally applicable technique for MPE protection (or "footprinting") analysis of specific DNA-protein complexes from a crude nuclear extract. We have used this method to identify the nucleotides of the immunoglobulin (Ig) heavy chain promoter region that are involved in complex formation with a protein that binds the octameric sequence ATGCAAAT, and we compare our results to those obtained previously using DNase I.