Another regulatory element located upstream of the gene is an enhancer. Enhancers function as a "turn on" switch in gene expression and will activate the promoter region of a particular gene while silencers act as the "turn off" switch. Though these two regulatory elements work against each other, both sequence types affect the promoter region in very similar ways. Because silencers have not been thoroughly identified and analyzed, the extensive research on enhancers has aided biologists in understanding the mechanics of the silencer. Enhancers can be found in many of the same areas that silencers are found, such as upstream of the promoter by many kilobase pairs, or even downstream within the intron of the gene. DNA looping is also a model function used by enhancers in order to shorten the proximity of the promoter to the enhancer. Enhancers also function with transcription factors in order to initiate expression, much like silencers can with repressors.