Thymine is one of the four nucleobases in the nucleic acid of DNA and can be a target for actions of 5-fluorouracil (5-FU) in cancer treatment, with a Km of 2.3 μM. Total inhibition of 5-FU degradation occurred at a uridine concentration of 10 microM, whereas thymidine was found to be a much less potent noncompetitive inhibitor of pyrimidine base degradation (Ki 24 microM) [2]. Thymine methyls can provide contact points via van der Waals interactions with amino acid side chains of specific DNA binding proteins[3]. The new base modification (Trex , thymine ring expunged) can form under physiological conditions, and is resistant to the action of common repair machineries[4]. Oxidation of DNA causes chemical reactions that result in remote damage (mutation) to a nucleobase. Normally this reaction occurs at guanine, but in oligonucleotides that lack guanines, or when the DNA contains a thymine-thymine mispair, reaction occurs primarily at thymine notwithstanding its high oxidation potential[5].
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