Scientists discovered that some viruses swap out one of their base genetic letters for a new fifth letter in a study published in a trio of articles in Nature.
All life on earth is made of genomes built of various combinations of the same four letters that make up DNA: A (adenine), T (thymine), C (cytosine) and G (guanine). A and T are always paired, and C and G are always paired.
"It's hard to imagine something more fundamental," said Floyd Romesberg, a synthetic biologist at Sanofai.
In 1977, researchers in the Soviet Union were examining a virus that affects photosynthetic bacteria when they found that all the A's in the genome had disappeared, and in their place was an alternative base they named Z.
Testing revealed that Z is a modification of A. It is an adenine with an extra attachment. Z paired with T instead of A and together, they formed a triple bond that was more stable than the A-T pairing.
In the early 2000's Philippe Marlière, a geneticist at the University of Evry in France, sequenced the genome the Soviet Union had found and compared it to other genomes of viruses in the database. He was assisted by research teams in Illinois and China.
"My instinct told me this is not just an anecdote," he said.
The research teams found Z in more than 200 phages (viruses that solely kill bacteria), as well as a key enzyme in Z that kills A.
Z seems to have evolved in order to help the viruses evade the defenses put up by the bacteria they kill.
Marlière's team has been trying to modify T in order to create E. coli for years. Huimin Zhao, a chemist at University of Illinois, is trying to get E. coli to incorporate Z in the same way the viruses do.
The study is changing the way we thing of genomic change and evolution in DNA because it shows that this kind of genomic spread could be more common than previously thought.
"Here was this wonderful validation that right under our noses, nature has been expanding," said Stephen Freeland, a biologist at the University of Maryland.