A unified architecture of transcriptional regulatory elements

• Recent results challenge the notion that promoters and enhancers are distinct entities.
• Enhancers can independently work as promoters.
• Gene promoters can have enhancer activity.
• The primary function of a regulatory element is context dependent.
• We propose a unified model of regulatory elements.

Gene expression is precisely controlled in time and space through the integration of signals that act at gene promoters and gene-distal enhancers. Classically, promoters and enhancers are considered separate classes of regulatory elements, often distinguished by histone modifications. However, recent studies have revealed broad similarities between enhancers and promoters, blurring the distinction: active enhancers often initiate transcription, and some gene promoters have the potential to enhance transcriptional output of other promoters. Here, we propose a model in which promoters and enhancers are considered a single class of functional element, with a unified architecture for transcription initiation. The context of interacting regulatory elements and the surrounding sequences determine local transcriptional output as well as the enhancer and promoter activities of individual elements.