Towards a new era of synthetic genetics

NOTE: this is a short post since this particular study has already been extensively discussed all over the scientific blogosphere, see for example this post. Here I just want to give a very general overview for those who may have not yet heard about this. I think my writer friends in particular will be extremely intrigued by this news.

In life as we know it, the storage and propagation of genetic information relies on two molecules: RNA and DNA. Both are made of building blocks called nucleotides, which are in turn composed of a nitrogenous base, a five-carbon sugar, and one phosphate group. The sugar in the RNA nucleotide is called ribose, and the one in the DNA nucleotides deoxyribose.

Most likely, the very first forms of life had RNA only. Being a single stranded molecule, it is less complex than DNA, but also less stable. As life became more complex, it evolved towards a more complex molecule. But have RNA and DNA always been the only two existing molecules capable of heredity and evolution?

In order to address the question, Pinheiro et al. [1] studied six new molecules (XNAs, for xeno nucleic acids) with the capability to store and propagate genetic information. The molecules were obtained using alternative sugar-like components in lieu of the five-carbon sugar. Synthetic nucleic acids are only the starting point. The key point the researchers had to address was: can these be synthesized back and forth from DNA? Because you see, the way genetic information is stored and passed on is through back and forth transcription between DNA and RNA so that proteins can be made.

Indeed, Pinheiro et al. engineered special polymerase enzymes able to do exactly that: reverse transcribe XNA into DNA and, viceversa, forward transcribe DNA into XNA.

"All six XNAs studied by Pinheiro et al. bind to complementary RNA and DNA and are resistant to degradation by biological nucleases. Construction of genetic systems based on alternative chemical platforms may ultimately lead to the synthesis of novel forms of life [2]."

I can see the imagination of a few people out there running wild. Yes, it is indeed wild. Think of the possibilities. Pinheiro and colleagues call this field of synthetic genetics a "route to novel sequence space."

Of course, this is just a first step. Let's not forget that life as we know it took billions of years to evolve from those first molecules of RNA. In my previous post I quoted Waddington's metaphor who compared the evolution and diversification of cells to marbles rolling down a rugged landscape. Gravity is the driving force and the pits and inclines are the constraints. What is to happen, though, if we, humans, start changing this landscape?

[1] Pinheiro, V., Taylor, A., Cozens, C., Abramov, M., Renders, M., Zhang, S., Chaput, J., Wengel, J., Peak-Chew, S., McLaughlin, S., Herdewijn, P., & Holliger, P. (2012). Synthetic Genetic Polymers Capable of Heredity and Evolution Science, 336 (6079), 341-344 DOI: 10.1126/science.1217622

[2] Joyce, G. (2012). Toward an Alternative Biology Science, 336 (6079), 307-308 DOI: 10.1126/science.1221724