If there is one rule in biology, it is that there is an exception to every rule. This includes even the basic biochemistry of DNA, which was once thought to be universal. On this episode, host Lauren Richardson and Judy Savitskaya (a16z bio deal team member and synthetic biology expert), discuss the results and implications three related articles co-published in Science, which all advance our understanding of a very unique kind of DNA. 

If you open any biology text book, it will say that the genetic code is made up of 4 bases: Adenine, Thymine, Cytosine, and Guanine, or ATCG. But, back in 1977, scientists discovered a phage — the technical term a virus that infects bacteria — that encodes its genome in ZTCG. Z is a derivative of A that has an extra amino group tagged on, and while that may sound minor, it changes some of the key properties of DNA. These three new articles seek to understand how Z is made and how it is incorporated into DNA. This is essential information for taking Z from a weird, wild bio story into a practical application. The conversation covers what makes Z different than other bases, what these three articles reveal about the synthesis and polymerization of Z, and how we can use use Z in a wide range of applications, from bio-containment to new therapeutics to DNA storage.

The three articles discussed are:

"A widespread pathway for substitution of adenine by diaminopurine in phage genomes" by  Yan Zhou, Xuexia Xu, Yifeng Wei, Yu Cheng, Yu Guo, Ivan Khudyakov, Fuli Liu, Ping He, Zhangyue Song, Zhi Li, Yan Gao, Ee Lui Ang, Huimin Zhao, Yan Zhang, and Suwen Zhao

"A third purine biosynthetic pathway encoded by aminoadenine-based viral DNA genomes" by Dona Sleiman, Pierre Simon Garcia, Marion Lagune, Jerome Loc’h, Ahmed Haouz, Najwa Taib, Pascal Röthlisberger, Simonetta Gribaldo, Philippe Marlière, and Pierre Alexandre Kaminski

"Noncanonical DNA polymerization by aminoadenine-based siphoviruses" by  Valerie Pezo, Faten Jaziri, Pierre-Yves Bourguignon, Dominique Louis, Deborah Jacobs-Sera, Jef Rozenski, Sylvie Pochet, Piet Herdewijn, Graham F. Hatfull, Pierre-Alexandre Kaminski, and Philippe Marliere