What is the Difference Between Enhancer and Promoter

The main difference between enhancer and promoter is that the enhancer is the DNA sequence to which the activators bind whereas the promoter is the DNA sequence to which RNA polymerase and other basal transcription factors bind. Furthermore, enhancer is responsible for increasing the rate of transcription while promoter is responsible for the initiation of transcription.

Enhancer and promoter are the two, short DNA sequences that serve as the regulatory elements of a gene. Their main function is to regulate transcription.

Key Areas Covered

1. What is Enhancer
     – Definition, Features, Function
2. What is Promoter
     – Definition, Features, Function
3. What are the Similarities Between Enhancer and Promoter
     – Outline of Common Features
4. What is the Difference Between Enhancer and Promoter
     – Comparison of Key Differences

Key Terms

Enhancer, Promoter, Rate of Transcription, RNA Polymerase, Transcription Factors, Transcription Initiation

What is Enhancer

An enhancer is a cis-acting element involved in increasing the activity of a particular promoter. It is a short DNA sequence of about 50-1500 bp and the transcription factors called activators can bind to it. The location of the enhancer can be up to 1 Mbp away from the promoter. It also can be upstream or downstream to the promoter. Through the location is far away from the promoter, enhancers are spatially close to the promoter, allowing the interactions with RNA polymerase and basal transcription factors. The activators bound to the enhancer region then bind with a mediator complex, which in turn recruit the RNA polymerase and the basal transcription factors to the promoter site. The orientation of the enhancer sequence has no influence on this action.

Figure 1: Enhancer

The antagonists of the enhancers are the silencers, which can bind to the transcription factors called suppressors. Suppressors can down-regulate the level of transcription.

What is Promoter

Promoter is one of the main regulatory element of the gene which initiates the transcription. It is located near the gene, upstream to the codon sequence. The size of the promoter can be 100-1000 bp. The specific DNA sequences called response elements provide initial binding sites for both RNA polymerase and transcription factors which recruit RNA polymerase. RNA polymerase is the enzyme responsible for the transcription, polymerizing complementary RNA nucleotides to synthesize a mRNA molecule.

Figure 2: Promoter

Bacterial RNA polymerase associated with sigma factor can bind to the promoter. Sigma factor is a bacterial transcription initiation factor. In eukaryotes, around 7 different basal transcription factors have to be bound to the promoter to recruit RNA polymerase.

Similarities Between Enhancer and Promoter

• Enhancer and Promoter are two, short DNA sequences which can occur upstream to the codon sequence of the gene.
• They occur in both eukaryotes and prokaryotes.
• Also, different types of transcription factors bind to both DNA sequences.
• Furthermore, the main function of the two DNA sequences is to regulate transcription.

Difference Between Enhancer and Promoter

Definition

Enhancer refers to the DNA sequence which increases the level of transcription of a gene whereas promoter refers to the DNA sequence which initiates transcription of a particular gene.

Location

An important difference between the enhancer and promoter  is that, an enhancer can be located upstream or downstream to the gene while a promoter occurs upstream to the gene in the same chromosome.

Bind to

Furthermore, transcription activators bind to the enhancer while RNA polymerase and basal transcription factors bind to the promoter. This is a major difference between the enhancer and promoter.

Role

Another difference between the enhancer and promoter is that the enhancers are involved in increasing the level of transcription while promoters are involved in controlling the transcription starts.

Orientation

Moreover, the function of the enhancer does not depend on the orientation while the function of the promoter completely depends on the orientation.

Conclusion

An enhancer is a cis-regulatory element to which activators bind in order to increase the level of transcription. It can be located in a short or long distance to the gene controlled by the enhancer. On the other hand, a promoter is the DNA sequence to which the RNA polymerase binds along with the basal transcription factors. It is closely located to the gene regulated by the promoter. The main difference between the enhancer and promoter is the role and the location with respect to the gene.

Reference:

1. “Enhancer (Genetics).” Enhancer-Genetics, ScienceDirect, Available Here
2. “Promoters.” Addgene, Available Here

Image Courtesy:

1. “Figure 16 04 01” By CNX OpenStax –  (CC BY 4.0) via Commons Wikimedia  
2. “Reporter gene” (CC BY-SA 3.0) via Commons Wikimedia