Figure 4.

Binding of radiolabeled probe to pUC18 is specifically competed by pMII-MAR, a 2974 bp MAR sequence containing plasmid. To determine the relative specificity of probe binding to a MAR sequence versus pUC18, mobility shift reactions containing M059K nuclear extract (0.5 µg) and ³²P-labeled probe (1 ng) were preincubated with closed circular pUC18 (0.5 µg) for 10 min before addition of closed circular pMII-MAR in increasing amounts as indicated. Duplicate sets of reactions were performed. Both sets were separated in parallel 1.5% agarose gels. One set (autoradiogram) was dried for autoradiography, while the other set (ethidium bromide stained) was stained with 1 mg/ml ethidium bromide and photographed. The position of pUC18 is indicated by a black arrow and the pMII-MAR by a white arrow.