Life created with two synthetic bases for 6 DNA letters with Original Four G, T, C, A and now X and Y and this expands amino acids from 20 to 172

From the moment life gained a foothold on Earth the diversity of organisms has been written in a DNA code of four letters. The latest study moves life beyond G, T, C and A – the molecules or bases that pair up in the DNA helix – and introduces two new letters of life: X and Y.

Romesberg started out with E coli, a bug normally found in soil and carried by people. Into this he inserted a loop of genetic material that carried normal DNA and two synthetic DNA bases. Though known as X and Y for simplicity, the artificial DNA bases have much longer chemical names, which themselves abbreviate to d5SICS and dNaM.

In living organisms, G, T, C and A come together to form two base pairs, G-C and T-A. The extra synthetic DNA forms a third base pair, X-Y. These base pairs are used to make genes, which cells use as templates for making proteins.

Romesberg found that when the modified bacteria divided they passed on the natural DNA as expected. But they also replicated the synthetic code and passed that on to the next generation. That generation of bugs did the same.

“What we have now, for the first time, is an organism that stably harbours a third base pair, and it is utterly different to the natural ones,” Romesberg said. For now the synthetic DNA does not do anything in the cell. It just sits there. But Romesberg now wants to tweak the organism so that it can put the artificial DNA to good use.

Nature – A semi-synthetic organism with an expanded genetic alphabet

Read more »