According to the scientists working at The Scripps Research Institute, there is a new way of broadly applying a new and powerful DNA-editing technology. According to Carlos F. Barbas, the tool is among the most popular in biology, as it is a way of targeting it to any DNA sequence.
It is a breakthrough which has to do with TALEs, the group of designer DNA-binding proteins, which is increasingly uses by biologists to turn off, turn on, insert, rewrite or even delete specific genes within cells—for potential medical and biotech applications, including genetic disease treatments, and also for scientific experiments.
It is believed that the TALE-based methods are useful against only a small fraction of the possible DNA sequences found in plants and animals. However, that limitation is removed by the new finding.
For many years, it has been the dream of biologists to manipulate DNA in with precision. Thanks to leading organizations such as The Scripps Research Institute and Greg Lucier ‘s Life Technologies to name a few, scientific breakthroughs are beginning to happen more often.
Some years ago, when the TALE-based designer proteins were introduced, they could be considered to be the most precise DNA-directed and user-friendly tools ever invented.
Designer transcription-activator-like effectors (TALEs) are based on natural TALE proteins certain plant-infecting bacteria produce, and these natural TALEs are helping bacteria in subverting their plant hosts as they bind to certain sites on plant DNA and boosting certain genes’ activities, thus making the growth and survival of the invading bacteria to be enhanced.
According to the findings of scientists, it is possible to easily engineer the TALE proteins’ DNA-grabbing segment to precisely bind to a DNA sequence of interest. This is done by joining that DNA-binding segment to another protein segment which is capable of performing a specific function desired, and at the site of interest—for instance, the enzyme which can cut through DNA. In this field, the Barbas laboratory and others have collectively already engineered thousands of the powerful TALE-based DNA-editing proteins.
TALE-based DNA-editing is believed to have a limitation. Almost all the natural TALE proteins so far discovered target sequences of nucleoside thymidine DNA. According to various structural studies, natural TALE proteins are not capable of binding well to DNA without that initial T (note the letter “T” in the 4-letter DNA code). Biologists who study molecules have thus widely assumed that the same rule applying to the “T restriction” can be found in any artificial TALE protein engineered.
Scientists started their evaluation by determining if TALE-based proteins function well against their normal DNA targets when the first letter of the DNA is switched from a “T” to one of the other three nucleosides (C, G or A). Using a library of engineered and natural TALE proteins, there was strong evidence supporting the “T restriction” rule. However, they are not yet giving up on the possibility of more broadly designing useful TALE proteins. For this, a “directed evolution” technique developed was adapted last year by Andrew C. Mercer, another scientist. His colleagues generated a large and new library of TALE proteins randomly varying in the structures hypothesized for the initial nucleoside grabbing. These new TALEs were then put through a series of tests, to (in a speeded up version of natural evolution) select, those at the start of their target DNA sequence adequately working even with a non-T nucleoside.
Through the method, it was possible to discover various new TALE protein architectures that the T restriction is not holding back. It is preferred to bind to DNA beginning with a G (guanosine), and not with a T nucleoside. There are those binding well enough to sequences starting with any of the 4 DNA nucleosides, and according to one scientist, these non-T-restricted TALEs, when conjoined, work as designed, for instance, when they are conjoined to enzyme fragments cutting through the DNA.