A nucleobase whose skeleton is derived from pyrimidine.
| Member | Definition | Role |
|---|
| alpha-putrescinylthymine | An N-substituted putrescine that is thymine in which a hydrogen of the methyl group has been replaced by one of the amino groups of putrescine. It replaces about half of the thymine residues in the DNA of bacetriophage phiW-14. | alpha-putrescinylthymine |
| cytosine | An aminopyrimidine that is pyrimidin-2-one having the amino group located at position 4. | cytosine |
| isocytosine | An aminopyrimidine in which the pyrimidine ring bears amino and hydroxy substituents at positions 2 and 4, respectively. | 2-amino-4-hydroxypyrimidine |
| thymine | A pyrimidine nucleobase that is uracil in which the hydrogen at position 5 is replaced by a methyl group. | thymine |
| uracil | A common and naturally occurring pyrimidine nucleobase in which the pyrimidine ring is substituted with two oxo groups at positions 2 and 4. Found in RNA, it base pairs with adenine and replaces thymine during DNA transcription. | uracil |