DNA scissors cleave their comrades.

The primary function of DNA is to bear information, but scientists have found that some DNA can act as enzymes to catalyze reactions. Now, researchers at Yale University have synthesized a DNA structure that can snip itself or other DNA strands in two. Functionally, these deoxyribozymes are cousins of protein enzymes known as restriction endonucleases. Nir Carmi, Shameelah R. Balkhi, and Ronald R. Breaker report their finding in the March 3 Proceedings of the National Academy of Sciences.

The researchers use a technique called in vitro evolution to screen sequences of DNA for catalytic properties. Starting with a pool of DNA molecules, each containing a random sequence about 50 bases long, they isolated groups of DNA that had the ability to cleave themselves. By purifying and amplifying those strands, then repeating the process many times, the researchers eventually found 27 molecules that efficiently clipped themselves in half. All of those DNA strands share a particular sequence, 21 bases long, that is essential to its enzymatic behavior, the researchers found.

They then took the experiment a step further and designed several DNA molecules to cut other ones at specific places. The molecules did so at the same rate as the original, self-cleaving DNA.

Scientists know that RNA molecules called ribozymes catalyze reactions. Establishing that DNA can also act as an enzyme is important in the study of how life on Earth originated. Presumably, the complete protein synthesis machinery now in cells did not exist initially, and nucleic acids had to perform some of the functions that enzymes do today (SN: 8/10/96, p. 87).

Also, the authors note, "catalytic DNAs may offer distinct advantages over natural protein enzymes for operation under nonbiological conditions." Engineered deoxyribozymes would not only be easier to synthesize than protein catalysts but could offer improved properties, such as stability at high temperatures.