How Does an Enhancer Work?

Reviewed on 1/28/2021

Enhancer and DNA
In the genes, there are some regions that enhance the transcription, known as enhancers.

Enhancers are regulatory deoxyribonucleic acid (DNA) sequences that provide binding sites for proteins that help activate transcription (formation of ribonucleic acid [RNA] by DNA). When the proteins that have a special affinity for DNA (DNA-binding protein) bind to an enhancer, the shape of the DNA changes. This change occurs to allow the interaction between the activator bound to the enhancers and transcription factors bound to the promoter region, leading to RNA production.

Enhancers can increase the expression of genes in their vicinity. There are several features of enhancers, which include:

  • They function over a vast distance from the target gene.
  • They are orientation dependent. For example, enhancers would still affect gene expressions when inverted.
  • They are often associated with over-expressed genes. For example, immunoglobulin genes often have associated enhancers.

What is an enhancer?

In the genes, there are some regions that enhance the transcription, known as enhancers. These enhancers may not necessarily be close to the genes that they modify. Enhancers are regulatory noncoding deoxyribonucleic acid (DNA) sequences that provide binding sites for proteins that help activate transcription.

Some of the examples of enhancer include:

  • HACNS1: This gene has contributed to the evolution of the human thumb.
  • GADD45G: This gene regulates brain growth in chimpanzees and other mammals but not in humans.

What is a noncoding DNA?

In the human body, only 1% of deoxyribonucleic acid (DNA) is made up of protein-coding genes. The other 99% is noncoding. Noncoding DNA does not provide directions for making proteins. Scientists once assumed that noncoding DNA was scrap with no known purpose. However, it is becoming evident that at least some of this DNA is vital to the function of cells, particularly to control gene activity. The regular elements present in the DNA sequences provide sites for specialized proteins (called transcription factors) to attach (bind) and either activate or suppress the process by which the genes are turned into proteins (transcription). Enhancers are one of the types of regulatory elements present in noncoding DNA. Other regulatory elements include:

  • Promoters provide binding sites for the protein machinery that carries out transcription.
  • Silencers provide binding sites for proteins that repress transcription.
  • Insulators supply binding sites for proteins that control transcription in several ways.

What is a gene expression?

Gene expression is a process where the genes are used to make proteins. The creation of proteins mainly occurs by the transcription of deoxyribonucleic acid (DNA) and translation of messenger ribonucleic acid (mRNA). There is the processing of proteins after the synthesis.

Regulation of gene expression is necessary to ensure that the correct proteins are made when and where they are needed.

Regulation of gene expression has two functions:

  1. Development: Regulation of gene expression is extremely crucial during the early development of an organism. Regulatory proteins or transcription factors must turn on certain genes in a specific cell at the correct time for the proper development of organs and organ systems. One example of regulatory protein is Homeobox genes involved in the regulation of gene expression during development.
  2. Cancer: Some types of cancer occur due to alteration in genes that control the cell cycle. Mutations may occur in two types of regulatory genes:
    • Proto-oncogenes are genes that help cells divide. When these genes mutate to become oncogenes, the cells keep on dividing out of proportion, leading to cancer.
    • Tumor suppressor genes stop or slow down cell division. When these genes mutate, it can no longer stop cell division, leading to abnormal cell division.

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References
Wakim S, Grewal M. 6.7: Regulation of Gene Expression. The California State University. https://bio.libretexts.org/Bookshelves/Human_Biology/Book%3A_Human_Biology_(Wakim_and_Grewal)/06%3A_DNA_and_Protein_Synthesis/6.07%3A_Regulation_of_Gene_Expression

Medline Plus. What Is Noncoding DNA? https://medlineplus.gov/genetics/understanding/basics/noncodingdna/

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