A potent GAL4 derivative activates transcription at a distance in vitro

Transcription of a typical eukaryotic gene by RNA polymerase II is activated by proteins bound to sites found near the beginning of the gene as well as to sites, called enhancers, located a great distance from the gene. According to one view, the primary difference between an activator that can work at a large distance and one that cannot is that the former bears a particularly strong activating region; the stronger the activating region, the more readily the activator interacts with its target bound near the transcriptional start site, with the intervening DNA looping out to accommodate the reaction. One alternative view is that the effect of proteins bound to enhancers might require some special aspect of cellular or chromosome structure. Consistent with the first view, an activator bearing an unusually potent activating region can stimulate transcription of a mammalian gene in a HeLa nuclear extract when bound as far as 1.3 kilobase pairs upstream or 320 base pairs downstream of the transcriptional start site.