ALLOSTERIC DEOXYRIBOZYMES CATALYZE SPECIFIC REACTIONS
Because some RNA has catalytic properties, researchers investigated whether DNA has catalytic potential. Although no natural catalytic DNA molecules are known, DNA nonetheless has the ability to catalyze various reactions in a manner similar to RNA-based ribozymes. Indeed, in vitro selection was used to create a deoxyribozyme that can split thymine dimers caused by UV radiation of DNA. Different organisms have various mechanisms to deal with these dimers. For example, excision repair removes the damaged strand and replaces it with new DNA. Another mechanism involves photolyase enzymes, which are activated by light.
These enzymes recognize and repair thymine dimers in response to blue light.
In order to identify a DNA sequence that could accomplish the photolyase reaction, in vitro selection was carried out on a pool of random DNA oligonucleotide sequences. The random sequences were first linked to a substrate that consisted of two DNA oligonucleotides joined via a thymine dimer. If a random oligonucleotide split the thymine dimer after exposure to blue light, then the overall length of the DNA construct would be smaller. The smaller species were isolated by gel electrophoresis. This was successful, and a specific deoxyribozyme (UV1C) that could catalyze a photolyase reaction was identified (Fig. 5.30).