Abstract

Enhancer elements are short stretches of nucleotides operationally defined by their cis‐acting ability to increase the transcription of nearby genes. They function relatively independently of position, orientation, and distance. Some show narrow tissue specificity while others permit constitutive expression in many different cell types. Although the first enhancer was described for simian virus 40 (SV40) more than five years ago, its mechanism of action has remained unclear. This review describes some of the models proposed to explain the physical role of enhancers in eukaryotic transcription.