Insulators. Eukaryotic promoters have many regulatory elements that require DNA looping across long distances. Shown here are two genes, A and B, each with several activator-binding sites. When the regulatory sites for gene A are filled, the activators act on the promoter of gene A, but the insulator sequence blocks their action on the promoter of gene B. Insulators have bound proteins that enable the insulator function (see Chapter 21).