https://doi.org/10.1351/goldbook.N04254
The heterocyclic pyrimidine and purine compounds which are constituents of all @[email protected] Adenine (A), guanine (G) and cytosine (C) are found in both @[email protected] and @[email protected], thymine (T) is found (primarily) in @[email protected] and uracil (U) only in @[email protected]