Similar mechanism of action for enhancer-blocking insulators; chromatin loop domains are formed in the nucleus that separates the enhancer and the promoter of a target gene. Loop domains are formed through the interaction between enhancer-blocking elements interacting with each other or securing chromatin fibre to structural elements within the nucleus. The action of these insulators is dependent on being positioned between the promoter of the target gene and the upstream or down stream enhancer. The specific way in which insulators block enhancers is dependent on the enhancers mode of action. Enhancers can directly interact with their target promoters through looping (direct-contact model), in which case an insulator prevents this interaction through the formation of a loop domain that separates the enhancer and promoter sites and prevents the promoter-enhancer loop from forming. An enhancer can also act on a promoter through a signal (tracking model of enhancer action). This signal may be blocked by an insulator through the targeting of a nucleoprotein complex at the base of the loop formation.