Question

What effect does the hypermethylation of promoter regions typically have on gene expression?

• A. Activation of transcription.
• B. Silencing of transcription.
• C. No effect on transcription.
• D. Increased translational efficiency.

Hint:

Remember this simple epigenetic rule: \textbf{Methylation Mutes}. High levels of DNA methylation in a promoter region generally lead to gene silencing. Conversely, demethylation or hypomethylation is associated with gene activation.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The question asks about the role of DNA methylation, a key epigenetic modification, in regulating gene expression. Specifically, it focuses on the effect of hypermethylation (an excess of methylation) in the promoter region of a gene.
Step 2: Detailed Explanation:


DNA methylation is the addition of a methyl group (-CH₃) to the DNA molecule, typically at CpG sites (a cytosine nucleotide followed by a guanine nucleotide).
The promoter is a region of DNA where transcription is initiated. It's the binding site for RNA polymerase and transcription factors.
Hypermethylation of a gene's promoter region is a well-established mechanism for gene silencing. It works in two main ways:

The methyl groups can physically block the binding of transcription factors and RNA polymerase to the promoter, thus preventing transcription from starting.
Methylated DNA can be recognized and bound by specific proteins called methyl-CpG-binding domain proteins (MBDs). These proteins, in turn, recruit histone deacetylases (HDACs) and other chromatin-remodeling proteins. This leads to the compaction of chromatin into a condensed, inactive state (heterochromatin), making the gene inaccessible for transcription.

Therefore, hypermethylation of the promoter is strongly associated with the repression or silencing of transcription.
Step 3: Final Answer:
The typical effect of hypermethylation of promoter regions is the silencing of transcription.