Practice question

Discriminating whether two different proteins bind same cis-regulatory element requires resolution of distinct complexes by size. Electrophoretic Mobility Shift Assay allows incubation of radiolabeled probe with each protein individually and in combination; each protein-DNA complex shows unique retarded mobility. Co-occupancy yields ternary complex with further retarded or intermediate mobility compared to binary complexes. Competition with unlabeled DNA and antibody supershift further validates specificity. ELISA and Western blot detect proteins without DNA localization, while ChIP shows in vivo occupancy but lacks in vitro comparative resolution for same-site binding analysis.