| Promoter |
The core promoter is the DNA region to which transcriptional machinery binds [15]. It includes some of the following: TATA box, initiator element (Inr), and downstream promoter element [15]. The Inr is the most common feature, being present in approximately half of all promoters [91]. Proximal promoter elements typically lie immediately upstream and within close proximity of the core promoter element [15]. |
| Enhancer |
Enhancers are specific DNA sequences that can regulate the activity of a promoter. The first enhancer was discovered in the SV40 tumour virus genome [92], and the first human enhancer was identified in the immunoglobulin heavy-chain locus [93]. Secondary enhancers have also been identified, and may act as ‘shadow enhancers’, ensuring that enhancer activity continues even if environmental conditions change and affect primary enhancer function [94–96]. |
| Super-enhancer |
Super-enhancers are defined as a grouping of enhancers that are situated within close proximity of each other and combinatorially bind transcription factors [76]. They tend to be differentiated from regular enhancers through a particular occupancy by cofactors [76]. However, there is still debate about whether super-enhancers really are a truly separate class of regulatory region, or whether they are simply strong enhancers that operate generally in the same way as a typical enhancer [97]. |
| Insulator |
Insulators are DNA sequences that act to partition the genome into regions defined by transcriptional activity [15]. |
| Silencer |
Silencers are specific DNA sequences that halt transcription by serving as binding sites for negative transcription factors (also called ‘repressors’) [15]. |
