Epigenetic Tags Lead To The Methylation of Promoters and Histones
- Gene expression is more than just the DNA sequence and also about how that sequence is regulated.
- This regulation is influenced by epigenetic tags, chemical modifications that alter gene activity without changing the DNA sequence itself.
- Two key examples are the methylation of promoters and histones.
Methylation Of DNA Promoters Represses Transcription
Definition
DNA methylation
DNA methylation involves the addition of a methyl group (–CH₃) to a cytosine base in DNA.
- This modification often occurs in regions called CpG islands, which are rich in cytosine-guanine pairs and are frequently found near promoters.
- It affects transcription by:
- Blocking transcription factor binding: Methylation of the promoter region can prevent RNA polymerase and other transcription factors from binding to the DNA, blocking the initiation of transcription.
- Recruiting repressor proteins: Methylated DNA can attract proteins that compact the chromatin structure, making it inaccessible to the transcription machinery.
In cancer cells, hypermethylation of tumor suppressor gene promoters can silence these critical genes, allowing uncontrolled cell growth.
Methylation of Histones Modulates Gene Expression
Definition
Histone
A protein that provides structural support for DNA in eukaryotic cells. Histones are positively charged, allowing them to interact with negatively charged DNA, helping to compact it into a condensed form called chromatin.
