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The small sequence of nucleotides present in DNA (deoxyribonucleic acid) that codes for a specific protein in the cell are called genes. The process by which these genes are expressed to produce mRNA (messenger ribonucleic acid) and proteins are called gene expression.

The gene expression is regulated by various factors or processes that either turn on or turn off the gene. Gene expression increases when the genes are turned on and decreases when the genes are turned off.

Histone acetylation and DNA methylation are some of the processes that are known to regulate gene expression.

The process in which an acetyl group is added to the histone tail of the histone protein is called histone acetylation. The acetylation reduces the electrostatic attraction between the DNA and histone proteins. This causes the chromatin structure to open up, which exposes the nucleosomal DNA.

The DNA becomes more accessible to the transcription machinery of the cell, thereby enhancing gene transcription. Thus, histone acetylation promotes the transcription of genes.

The process in which the methyl group is added to the cytosine bases of DNA and converts it into 5-methylcytosine is called DNA methylation. The methylation of DNA affects the interaction of DNA with proteins and transcription factors of the cell.

DNA regions that are not transcriptionally active are heavily methylated as compared to areas that are actively transcribed. Thus, DNA methylation turns off the genes, thereby reducing the expression of genes.

As a result, DNA methylation regulates gene expression.