nucleotide bases
The heterocyclic pyrimidine and purine compounds which are constituents of all nucleic acids. Adenine (A), guanine (G) and cytosine (C) are found in both DNA and RNA, thymine (T) is found (primarily) in DNA and uracil (U) only in RNA.
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 147 (