Difference Between Inducible and Constitutive Promoter

The key difference between inducible and constitutive promoter is that the inducible promoter is a regulated promoter that is active only in response to specific stimuli while the constitutive promoter is an unregulated promoter which is active in all circumstances.

Promoter is an essential part of a gene. It is a DNA sequence located near and upstream to the transcription initiation site of the gene. Promoters may have 100 to 1000 base pairs. They allow the binding of RNA polymerase (enzyme) and other necessary proteins (transcription factors which recruit RNA polymerase) to start transcription. There are different types of promoters. Inducible and constitutive promoters are two such types. Inducible promoters are regulated promoters that become active in the cell only in response to a specific stimulus. On the other hand, constitutive promoters are unregulated promoters that are active in all circumstances in the cell.

1. Overview and Key Difference
2. What is an Inducible Promoter
3. What is a Constitutive Promoter
4. Similarities Between Inducible and Constitutive Promoter
5. Side by Side Comparison – Primer vs Promoter in Tabular Form
6. Summary

What is an Inducible Promoter?

Inducible promoter is a regulated promoter which becomes on or active in the cell in response to specific stimuli. Therefore, these promoters are active only under certain circumstances. Unless it receives a stimulus, inducible promoter stays at inactive state. In the inactive state or off state, transcriptional factors or RNA polymerase cannot bind with the promoter. Once an inducer binds to the activator protein, activator protein binds with the promoter and makes it active to initiate transcription.

Inducible promoters activate in response to different stimuli such as light, temperature and chemical agents, etc. Based on the type of stimulus that activates the promoter, there are different types of inducible promoters as chemically inducible promoters, inducible temperature promoters and light-inducible promoters, etc. Chemically inducible promoters are the most common. Some inducible promoters are activated by alcohols, tetracycline, antibiotics, copper, steroid, etc. Temperature inducible, light-inducible, oxygen level, cold-inducible, heat-inducible and mechanical injury inducible promoters are also called physically inducible promoters.

Difference Between Inducible and Constitutive Promoter

Figure 01: Promoter

What is a Constitutive Promoter?

Constitutive promoter is an unregulated promoter which is active in vivo at all the circumstances. Therefore, these promoters carry out the transcription of associated genes continuously in the cell. The activities of these promoters are not affected by transcriptional factors. Regardless of the surrounding environment and the development stage of the organism, constitutive promoters allow the transcription of genes in all tissues. They are largely independent of environmental and developmental factors. Hence, these promoters are active across species and even across kingdoms.

In plants, constitutive promoters are used for the expression of transgenes. Generally, a cell requires tRNA, rRNA, RNA polymerase, ribosomal proteins continuously. The genes that produce these products have constitutive promoters. Some examples of constitutive promoters include plant ubiquitin promoter, rice actin 1 promoter, maize alcohol dehydrogenase promoter, etc. Opine promoter and CaMV 35S promoter are two more examples of constitutive promoters.

What are the Similarities Between Inducible and Constitutive Promoter?

Inducible and constitutive promoters are two of the four types of promoters.
They are DNA sequences located near the transcription initiation site of genes.
They facilitate the binding of RNA polymerase and transcription factors.

What is the Difference Between Inducible and Constitutive Promoter?

Inducible promoter is a regulated promoter that allows transcription of its associated genes only in certain circumstances in the cell. Constitutive promoter is an unregulated promoter which allows continual transcription of its associated genes. So, this is the key difference between inducible and constitutive promoter. Moreover, another difference between inducible and constitutive promoter is that the inducible promoters are affected by abiotic and biotic factors, while the constitutive promoters are largely independent of environmental and developmental factors.

Below info-graphic summarizes the differences between inducible and constitutive promoter in tabular form.

Summary – Inducible vs Constitutive Promoter

Inducible and constitutive promoters are two types of promoters. Inducible promoters allow the transcription of their genes only at certain circumstances in response to specific stimuli. They are regulated promoters. On the other hand, constitutive promoters allow continuous transcription of their associated genes. They are unregulated promoters. Thus, this is the key difference between inducible and constitutive promoter. Constitutive promoters are independent of environmental and developmental factors while inducible promoters are affected by the biotic and abiotic factors.

Reference:

1. Gearing, Mary. “Plasmids 101: Inducible Promoters.” Addgene Blog Share Science, Available here.
2. “Promoter (Genetics).” Wikipedia, Wikimedia Foundation, 27 Nov. 2020, Available here.