|Section2= |Section3= }} 5-Methylcytosine's a methylated form of cytosine in which a methyl group's attached to carbon 5, altering its structure without altering its base-pairing properties. In vivo 5-Methylcytosine's an epigenetic modification formed by the action of DNA methyltransferases. Its function varies significantly among species: In bacteria, 5-methylcytosine can be found at a variety of sites, and's often used as a marker to protect DNA from being cut by native methylation-sensitive… (More on 5-methylcytosine)