Experimental design. (A) A series of four plasmids was utilized in the experimental assay system. Functional components of the luciferase-reporter expression vectors are indicated: (Promoter-control) the minimal promoter-only control plasmid; (Enhancer-control) the control plasmid containing the enhancer. The insertion sites for silencer elements and enhancer-blocking (EB) sites are designated relative to the enhancer location. Expression levels are high for enhancer-driven expression (10–100×) and low for full repressive activity (1×). (B) The experimental options included the choice of promoter, cloning orientation, the function (assessed by virtue of the cloning position), and cell line.
