Index >> Deoxyribose Nucleic Acid - DNA >> Unusual Bases in DNA

Unusual Bases in DNA - Although the bases most commonly present in DNA are adenine, guanine, cytosine and thymine, other bases have also been found. In some viruses (e.g. PBS 1 and PBS 2) uracil occurs in place of thymine in DNA.

Also, in some bacterial viruses (bacterio-phages) cytosine is replaced by 5-hydroxymethyl-cytosine (HMC). The variations of C, A and G in DNA can be considered to be the result of methylation of these bases.