Slashdot Mirror
New Letters Added To the Genetic Alphabet
An anonymous reader writes with this excerpt from Quanta Magazine: [A]fter decades of work, [organic chemist Steven] Benner's team has synthesized artificially enhanced DNA that functions much like ordinary DNA, if not better. In two papers published in the Journal of the American Chemical Society last month, the researchers have shown that two synthetic nucleotides called P and Z fit seamlessly into DNA's helical structure, maintaining the natural shape of DNA. Moreover, DNA sequences incorporating these letters can evolve just like traditional DNA, a first for an expanded genetic alphabet.
In fact, the article continues, these new nucleotides can actually outperform their natural counterparts: "When challenged to evolve a segment that selectively binds to cancer cells, DNA sequences using P and Z did better than those without."
It is not clear how the new nucleotides act when transcribing proteins but assuming its at least as efficient as the 4 letter code it could be a very interesting option for artificial viruses. A virus engineered to be totally dependent on the new nucleotides could be used much more safely even inside humans where there is no supply of them, they could infect the cells, produce proteins and a huge immune response but not a single copy of their genetic material could be produced. Also in a controlled environment they would thrive (cheap production?) but without P-Z no danger of new virus production so safety would not need to be as strict.
Applications on real organisms probably will take much longer time, but the simplicity of virus would make it a natural first step.
They say the new DNA outperforms the standard DNA in evolving to meet the researcher's criteria. That means it changes more easily. In other words, it's less stable.
In most situations, what we want is stability. Nature needs some ability to mutate and evolve, but considering that the wrong mutations result in cancer and death, too high of a mutation rate leads to failure. I suspect this is particularly true in long-lived larger organisms.
Of course we did not evolve wheels neither. Almost all animals above worms are torii topologically. (The digestive tract is the hole in the ring). There is one bacteria that has a free spinning flagellum. So nature started on that kind of disjoint topology, but could not scale it beyond bacteria. Two symbiotic animals one providing a wheel with shaft and another providing the bearing, together could have formed a wheeled animal. But that never happened, there is no path in the fitness landscape to achieve that configuration. Is it something fundamental like this that prevented six letter DNA
Or, more prosaically, the drawbacks outweigh the benefits. After all computers use binary not tertiary numbers. The four letter DNA is technically a binary system. Two pairs. So even if this thing escapes the laboratory it won't thrive in the wild and wipe out all the present forms of life Comforting if it is so.
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
This is part of a broader DARPA driven effort to expand what biology is capable of.
The end goal is to be able to create new materials (better fuels, medicines, building materials, etc) using biology. This requires expanding the "toolkit" biology uses to incorporate biologically incompatible elements, chemicals and processes.
So, starting from the end: We want a better biofuel. To do that, we want proteins that can better incorporate inorganic catalysts and work at higher energies than existing biology. To do that, we need different amino acids and protein construction machinery. To do that, we want to expand DNA to code for these new amino acids.
This is a "good" DARPA project in that we're not able to do all of this yet. What this means is that technology is pushed forward significantly, and we're able to clearly identify the real challenges.