The main difference between positive and negative gene regulation is that in the positive gene regulation, genes undergo transcription whereas, in the negative gene regulation, the gene expression is normally blocked. Furthermore, in positive gene regulation, a transcription factor binds to the promoter region, enabling the binding of RNA polymerase to the promoter while, in the negative gene regulation, a repressor protein binds to the operator region, preventing the binding of RNA polymerase. 

Positive and negative gene regulation are the two stages of gene regulation. Generally, they help to synthesize gene products based on the requirements of the cell. 

Key Areas Covered 

1. What is the Positive Gene Regulation
     – Definition, Process, Importance
2. What is the Negative Gene Regulation
     – Definition, Process, Importance
3. What are the Similarities Between Positive and Negative Gene Regulation
     – Outline of Common Features
4. What is the Difference Between Positive and Negative Gene Regulation
     – Comparison of Key Differences

Key Terms 

Activator, Negative Gene Regulation, Operator Region, Positive Gene Regulation, Promoter, Repressor

What is Positive Gene Regulation 

Positive gene regulation is the process that turns on gene expression. Generally, to carry out transcription, RNA polymerase should bind to the promoter region of the gene. Basically, RNA polymerase is the enzyme responsible for the synthesis of mRNA based on the instructions encoded in the coding region of the gene. However, the binding of RNA polymerase into the promoter region in eukaryotes requires the presence of basal transcription factors. On the other hand, in prokaryotes, the enzyme binds to DNA without the help of basal transcription factors.

Figure 1: Positive Gene Regulation

Furthermore, the operator region of the gene can bind to other transcription factors, which serve as activators of gene expression. The operator regions bound to activators are called enhancers. It, in turn, recruits RNA polymerase to the promoter region for the initiation of transcription in both eukaryotes and prokaryotes. Therefore, positive gene regulation is the activation of transcription through the binding of activating transcription factors to the promoter region. 

What is Negative Gene Regulation 

Negative gene regulation is the second type of gene regulation responsible for turning off genes. Here, another type of proteins called repressors binds to the operator region of the gene. Then, this type of operator region is known as the silencer region. However, the binding of repressors to the operator region prevents the recognition of the promoter region by RNA polymerase. Therefore, the enzyme is unable to bind to the gene to initiate transcription.

Figure 2: Allosteric Regulation of Repressor

Generally, the regulation of both activators and repressors occurs through the binding of allosteric effectors to them. Here, the binding of these effectors to the activators enables the binding of activators to DNA. On the contrary, the binding of allosteric effectors to the repressors prevents repressors from binding to DNA. 

Similarities Between Positive and Negative Gene Regulation 

• Positive and negative gene regulation are the two stages of the regulation of gene expression. 
• They occur in both eukaryotes and prokaryotes. 
• Also, both help to synthesize gene products based on the amount required by the cell. 
• Therefore, they help cells to go through different stages, including the growth development, and reproduction. 
• Besides, different proteins bind to the regulatory region of the gene to regulate gene expression. 
• Moreover, these proteins occur in two physical stages; those who are able to bind to DNA and those who are unable to bind to DNA.  
• In both proteins, binding is regulated by allosteric effectors.  

Difference Between Positive and Negative Gene Regulation 

Definition 

Positive gene regulation refers to the type of gene regulation that enables the expression of genes, while negative gene regulation refers to the type of gene regulation that prevents the gene expression. Hence, this is the main difference between positive and negative gene regulation.

Type of Proteins Bind to the Regulatory Regions of the Gene 

In the positive gene regulation, transcription factors bind to the promoter region of the gene while, in the negative gene regulation, repressors bind to the operator region. 

Effect of the Allosteric effectors 

Furthermore, the binding of allosteric effectors enable the transcription factors to bind to DNA in positive gene regulation, while the binding of allosteric effectors prevents the binding of repressors to DNA in negative gene regulation. Thus, this is also a difference between positive and negative gene regulation.

Effect on Transcription 

Moreover, the binding of transcription factors enables the binding of RNA polymerase to the promoter region, and hence, positive gene regulation enables transcription. On the other hand, the binding of repressors to the operator region of the gene prevents the binding of RNA polymerase into the promoter region and hence, negative gene regulation prevents transcription of the gene. 

Importance

Another difference between positive and negative gene regulation is that positive gene regulation turns on genes, while the negative gene regulation turns off the gene.

Conclusion 

Positive gene regulation is the stage of gene expression that enables to proceed gene expression. Normally, it occurs through the binding of the activator proteins called transcription factors to the promoter region of the gene. Generally, the resultant complex interacts with RNA polymerase, initiating transcription. On the other hand, negative gene regulation is the second stage of gene expression, which terminates gene expression. However, it occurs through the binding of a repressor protein to the operator region of the gene. Generally, this binding prevents interactions with RNA polymerase. Therefore, it terminates gene expression. Hence, the main difference between positive and negative gene regulation is the process of regulation and importance. 

References:

1. Griffiths AJF, Miller JH, Suzuki DT, et al. An Introduction to Genetic Analysis. 7th edition. New York: W. H. Freeman; 2000. Positive and negative control. Available Here.

Image Courtesy:

1.  “Role of transcription factor in gene expression regulation” By Philippe Hupé – Emmanuel Barillot, Laurence Calzone, Philippe Hupé, Jean-Philippe Vert, Andrei Zinovyev, Computational Systems Biology of Cancer Chapman & Hall/CRC Mathematical & Computational Biology , 2012 (CC BY-SA 3.0) via Commons Wikimedia
2. “The lac Operon: An Inducer Operon” By OpenStax CNX (CC BY 3.0) via OpenStax College

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