The lexicon of life just got a little larger. According to a recent article from New Sceintist, researchers at the Scripps Research Institute in La Jolla, California, have created the world's first synthetic base pair. After about 10 years of research, Dr. Floyd Romesberg has designed two new molecules that are accurately and "naturally" incorporated into growing DNA strands by DNA Polymerases, called dSICS and dMMO2. This expands the 4 letter "alphabet" of DNA from 4 bases to 6. Borrowing high throughput screening methods usually employed by drug developers, Romesberg screened though about 3600 candidate molecules and found that dSICS and dMMO2 worked the best. Still, dSICS seemed to pair with itself better than with its intended partner. This meant that the two molecules underwent some 15 modifications to alter their pairing specificites until one change seemed to work - adding a methly group onto the side of dSICS (the base is more accurately named d5SICS). The two new bases act just like regular bases, as far as the cell is concerned.
But what good is this? Adding two new base pairs could give DNA the ability to code for a greater variety of amino acids, meaning a number of new proteins can be produced. This idea, however, is somewhat pointless - the genetic code already codes for the esscential amino acids; any "rare" amino acids are just altered versions of the core 20, modified through specific biochemical pathways. Cells already produce a vast variety of amino acids using the 4 bases we have now. Romesberg has his sights set on other uses for dSICS and sMMO2 - applications in building nanostructures, molecular computing, and highly specific primers or tags. Even more ambitiously, he sees his work as a step towards "increasing" evolution: "We want to import these into a cell, study RNA trafficking, and in the longest term, expand the genetic code and 'evolvability' of an organism."
This technology is far from becoming widely used, and there is still much work to be done to get dSICS and dMMO2 to be used for molecular applications. Nevertheless, the potential behind new synthetic bases will make then an incredibly useful tool in the future.