Figure 4. Binding of an EcRE fragment to protein. Panel A shows an electrophoretic mobility shift assay in which C7-10 nuclear extracts were incubated with end-labeled pSX206 DNA. Lane 1 shows migration of the probe in the absence of protein. Lane 2 contains nuclear protein from approximately 1 g of C7-10 cells, and Lane 3 contains nuclear protein and ~500 fold excess non- radioactive probe. Panel B shows a southwestern blot in which end-labeled pBBg184 DNA was incubated in the presence of 0 to 250-fold excess unlabeled DNA on individual nitrocellulose strips.