Difference Between Repressor and Corepressor

The key difference between repressor and corepressor is that repressor protein directly binds to the operator sequence of the gene and inhibits gene expression while corepressor protein binds to the repressor protein and indirectly regulates the gene expression.

Genes are the units of heredity. They have genetic information to make proteins. In order to make proteins, genes should be expressed via transcription and translation. Transcription factors should bind to promoters and enhancers and recruit RNA polymerase enzyme to initiate transcription. Gene expression can be regulated especially at the transcription level. The repressor is a protein that inhibits gene expression. Corepressor is a protein that indirectly regulates gene expression by binding to transcription factors. Repressors recruit corepressor complexes. In eukaryotes, both repressors and corepressors are proteins.

CONTENTS

1. Overview and Key Difference
2. What is Repressor
3. What is Corepressor
4. Similarities Between Repressor and Corepressor
5. Side by Side Comparison – Repressor vs Corepressor in Tabular Form
6. Summary

What is Repressor?

Repressor is a protein that binds to DNA or RNA and inhibits the expression of one or more genes. Often these repressor proteins bind with the promoter region or associated silencers. DNA binding repressor proteins prevent the binding of RNA polymerase to the promoter sequence of the gene and stop the transcription of gene sequence into mRNA.

RNA binding repressor proteins, on the other hand, block the translation of mRNA into proteins. Methionine repressor (MetJ) is an example of repressor protein. Lactose repressor protein (LacI), which controls the expression of lactose metabolic genes, is also an example of repressor protein.

What is Corepressor?

Corepressor is a protein that binds to the repressor protein and indirectly regulates gene expression. It is an effector molecule. They are able to activate repressors. Recruitment of corepressor is done by a repressor protein since they are incapable of binding with DNA independently. Corepressors compete with coactivators to the same binding sites and bind to transcription factors in order to inhibit gene expression. In prokaryotes, corepressors are small molecules. In humans, there are several dozen to hundreds of corepressors.  Generally, corepressors exist as corepressor complexes having multiple proteins.

What are the Similarities Between Repressor and Corepressor?

• In eukaryotes, repressors and corepressors are proteins that regulate gene expression.
• Repressors recruit corepressor complexes.
• Corepressor activates the repressor by binding with it.

What is the Difference Between Repressor and Corepressor?

Both repressor and corepressor regulate gene expression by inhibiting it. Repressor binds to pieces of DNA called operators in the gene while corepressor binds to the repressor. So, this is the key difference between repressor and corepressor. Repressor blocks the attachment of RNA polymerase to the promoter while corepressor competes with coactivators to bind transcription factors. Moreover, repressors bind to a gene’s operator DNA sequence while corepressors do not directly bind to DNA.

The following infographic summarizes the difference between repressor and corepressor in tabular form.

Summary – Repressor vs Corepressor

Both repressor and corepressor block gene expression. Corepressors bind with repressors and activate them in order to block gene expression. Repressor binds with the operator sequence of the gene and blocks the binding of RNA polymerase enzyme to the promoter. When RNA polymerase does not bind to the promoter of the gene, transcription is not initiated. In the end, gene expression is inhibited. Thus, this summarizes the difference between repressor and corepressor.

Reference:

1. “Repressor.” Wikipedia, Wikimedia Foundation, 9 Mar. 2020, Available here.
2. “Regulating Gene Expression.” SlideShare, 13 Nov. 2012, Available here.

Image Courtesy:

1. “Lac Operon” By T A RAJU – Own work (CC BY-SA 3.0) via Commons Wikimedia