Paused Pol II captures enhancer activity and acts as a potent insulator.

Enhancers act over many kilobase pairs to activate target promoters, but their activity is constrained by insulator elements that prevent indiscriminate activation of nearby genes. In the July 1, 2009, issue of Genes & Development, Chopra and colleagues (pp. 1505-1509) report that promoters containing a stalled Pol II are activated by enhancers, but these promoters also serve as insulators that block enhancers from reaching more distal genes. This new class of insulators provide critical clues to regulatory mechanisms.