What is the difference between DNA methylation and histone modification?

DNA methylation and histone modification are two epigenetic mechanisms that regulate gene expression.

DNA methylation involves the addition of a methyl group to the cytosine nucleotide in DNA, which can lead to the repression of gene expression. This occurs when the methyl group interferes with the binding of transcription factors to the DNA, preventing the initiation of transcription. DNA methylation is often associated with long-term gene silencing and is involved in processes such as X-chromosome inactivation and genomic imprinting.

Histone modification, on the other hand, involves the addition or removal of chemical groups to the histone proteins that make up the nucleosome. These modifications can alter the structure of the chromatin, making it more or less accessible to transcription factors and RNA polymerase. For example, acetylation of histones is associated with an open chromatin structure and increased gene expression, while methylation of histones can lead to either activation or repression of gene expression depending on the specific amino acid that is modified.

Overall, DNA methylation and histone modification are both important mechanisms for regulating gene expression and maintaining cellular identity. While they are distinct processes, they often work together to achieve precise control over gene expression patterns.