Figure 4.

EMSAs demonstrating that PPBF and SBF have distinct DNA-binding specificities. A. Restriction fragments encompassing the U4X enhancer, U4X PSE, U4B enhancer, or U4B PSE were end-labeled and incubated with 0, 1, or 3 μl of affinity-purified PPBF (as indicated above each lane); the formation of protein-DNA complexes was analyzed by electrophoresis in a native polyacrylamide gel. B. The same four DNA fragments were incubated with 0, 4, or 9 μl of affinity-purified SBF, an snRNA gene enhancer-binding protein; complex formation was analyzed as in A. C. Diagram showing the regions encompassed by the U4X distal, U4X proximal, U4B distal, and U4B proximal restriction fragments used in the EMSA analyses presented in A and B.