In plants, a form of this molecule can be cleaved by proteins from the DEMETER family. Combining this molecule with arabinose generates an anti·metabolite often used to treat acute myeloid leukemia. In a technique developed by Chuan He’s lab, the oxidation of a derivative of this molecule by TET proteins converts it into a 5-carboxyl form reactive to bisulfite. Enzymes from the AID/APOBEC family facilitate the (*) deamination of this molecule. This molecule, which is subjected to methylation by DNMTs during epigenetic control, is the lighter of the two nucleobases found at “island” sequences that it (-5[1])co-names. This pyrimidine can appear in both DNA and RNA, unlike thymine and uracil. For 10 points, name this nucleobase that pairs with guanine. ■END■ (10[2])