Put another nickel in
DNA has been given a fifth base, which can form stable yet switchable basepairs with itself.
Looking at the geometrical perfection of the DNA double helix, it is hard to imagine any way in which it could be improved. Nevertheless, researchers in California, US, have succeeded in creating a new and potentially useful kind of base pair.
Christopher Switzer's group at the University of California at Riverside designed a metal-coordinated base pair starting from a conventional adenine base.1
The researchers replaced the amino group with a pyridyl group, creating a bidentate nitrogen ligand, two of which could coordinate bivalent cations like copper, zinc or nickel. They incorporated a pair of the new bases into a short double helix held together by several conventional base pairs, and tested seven kinds of metal ions for their effect on the stability of the duplex. Nickel ions turned out to be the most stabilising with respect to thermal denaturation of the double helix.
The nickel-bound base pair is also more error-resistant than conventional AT and GC pairs. A mismatch with any of the other four bases destabilises the duplex to an extent comparable with the most severe clash between ordinary bases (CA).
Another advantage over conventional basepairs is that the nickel ion can be easily added or removed, allowing researchers to create a switchable DNA duplex for applications such as DNA architecture, robots, or computers. How useful the new base will be depends on whether DNA polymerases can replicate it correctly, to produce nickel-controlled DNA in unlimited amounts.
Switzer says his group is 'actively pursuing this possibility', although he has nothing yet to report. But even without a compatible polymerase, he says, 'the nickel base pair should be useful for both DNA architectural and robotic applications, given our ability to machine synthesise oligomers'.
Switzer's group has recently produced another nickel-liganded base pair from pyrimidines, giving DNA a sixth base.2
- C Switzer et al, Angew. Chem. Int. Ed., 2005, 44, 1529