An unnatural base pair (UBP) is a designed subunit (or nucleobase) of DNA which is created in a laboratory and does not occur in nature. DNA sequences have been described which use newly created nucleobases to form a third base pair, in addition to the two base pairs found in nature, A-T (adenine-thymine) and G-C (guanine-cytosine).
- Leconte, Aaron M., Gil Tae Hwang, Shigeo Matsuda, Petr Capek, Yoshiyuki Hari, and Floyd E. Romesberg. "Discovery, Characterization, and Optimization of an Unnatural Base Pair for Expansion of the Genetic Alphabet." Journal of the American Chemical Society 130.7 (2008): 2336-343. Print.