methylcytosine

Methylcytosine refers to a modified form of the DNA base cytosine. In this modification, a methyl group (CH3) is attached to the carbon atom at the fifth position of the cytosine ring. This epigenetic modification plays a crucial role in gene regulation in many organisms, including mammals. The most common form is 5-methylcytosine (5mC).

DNA methylation primarily occurs at CpG dinucleotides, where a cytosine nucleotide is followed by a guanine nucleotide. These CpG sites are often clustered in regions called CpG islands, which are frequently found in the promoter regions of genes. Methylation of cytosine in these promoter regions can lead to gene silencing, effectively turning genes off. This process is mediated by enzymes called DNA methyltransferases (DNMTs).

The pattern of DNA methylation is established during development and can be inherited through cell division. This epigenetic marking is dynamic, with mechanisms for both methylation and demethylation (removal of the methyl group). Aberrant DNA methylation patterns are associated with various diseases, including cancer, neurological disorders, and developmental abnormalities. Understanding methylcytosine is therefore vital for comprehending gene expression control and its implications in health and disease.