Figure 6.

EMSAs demonstrating the differential interaction of SBF with the U4B and U4X enhancers. Assays were performed by incubating 6 μl of affinity-purified SBF with a ³²P-labeled DNA fragment encompassing either the U4B enhancer (A and B) or the U4X enhancer (C and D). Incubation mixtures also contained as specific competitor DNA increasing amounts of either the unlabeled U4B fragment (A and C) or the unlabeled U4X fragment (B and D). In each case, the U4B fragment was a 20- to 30-fold more effective competitor than the U4X fragment. The autoradiograms in C and D are 3-fold longer exposures than those shown in A and B. The U4B and U4X distal DNA fragments are diagrammed in Fig. 4C.