Hachimoji DNA

The quest to find Extra-terrestrial Life using Synbio

Rohan Nath

Integrated PhD, Biological Sciences

The advantage of synthetic biology lies in the fact of how one can engineer a biological system to unravel the enigmas of the universe. Such is the case of Hachimoji DNA, where scientists have utilised the concepts of synthetic biology to modify DNA molecules to explain the possibilities of establishment of life forms on other planets.

Let's begin with a simple high school question, what is DNA? DNA, which stands for 'Deoxyribonucleic Acid' is a carrier of genetic information in all known organisms and many viruses. DNA forms strands with repeating monomers or units called nucleotides. A nucleotide is composed of a deoxyribose sugar attached to a phosphate group and one of four nitrogenous bases (Adenine (A), Guanine (G), Cytosine (C) and Thymine (T)). Two DNA strands can coil around each other to form a double-helical structure, wherein these nucleotides are arranged in a pattern, which contains the information that makes you, you! Specific pairs of nucleotides can form hydrogen bonds (base pairs) that makes this structure look like a ladder with the bases forming the rungs, and the sugar-phosphate moieties forming the backbone or skeleton. There are plenty of complexities in a DNA structure, but that's a subject for some other day.

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So, what is Hachimoji DNA?

In Japanese, “Hachi” means eight and “moji” means letter, together they imply ‘eight lettered DNA’. So, in Hachimoji DNA, there are eight different nucleotides instead of four as found in natural DNA. There are four types of base pairs in Hachimoji DNA, two natural base pairs, i.e., A binds with T and G binds with C along with two synthetically produced unnatural base pairs where P binds with Z and B binds with S.

Financed by the NASA, the research team led by Dr. Steven Benner in their laboratory at the Foundation for Applied Molecular Evolution made it possible to generate a synthetic DNA molecule from scratch with eight-letter genetic codes (A, T, G, C, P, Z, B and S) instead of four. Professor Andrew Ellington and his team of researchers from the University of Texas used an enzyme called T7 polymerase to transcribe (read the sequence of bases and use it to build an RNA molecule) the Hachimoji DNA. The corresponding RNA created a green fluorescent glow due to a spinach fluorescent RNA aptamer which binds to 3,5-difluoro-4-hydroxybenzylidene imidazolinone to produce the green glow.

You must be thinking, how did it assist us to find extra-terrestrial life. The short answer is, it didn’t! It widely broadened our horizon for the understanding of how extra-terrestrial life might’ve originated in the vast universe. We might’ve obtained P, Z, B and S bases synthetically in a lab, but imagine : what if they occur naturally in the environment of some distant planet? It implies that there must be numerous methods to store genetic information other than the four nucleotides which generally formulate our DNA. Hachimoji DNA provides scientists with fresh insights into the discovery of new life forms in outer space. It gives us a sort of clarity on what we should expect while looking for life in other planets.

Hachimoji DNA proves the possibility of the existence of a more advanced life form. How? Let us delve into a little mathematics to make it clear. Nothing too complicated. Imagine a DNA molecule with ten nucleotides. In our natural DNA, there are four different types of nucleotides present. Now, considering that every single type of nucleotide has an equal chance to be present, it provides us with 4^10 = 1,048,576 different types of unique sequences. In Hachimoji DNA, all eight types of nucleotide are likely to be expressed equally, providing us with 8^10 = 1,073,741,824 unique DNA sequences in a single molecule. This is 1024 times greater than a DNA sequence with four different nucleotides. The amount of information stored in a Hachimoji DNA molecule is immense!

In conclusion, I would like to quote a statement by one of the brilliant minds of the 21st century, Bill Gates, from his book, The Road Ahead, “DNA is like a computer program but far, far more advanced than any software ever created.” The capacity of a DNA molecule as a carrier of genetic information and as a backbone of biological evolution is extraordinary! The creation of Hachimoji DNA might be just pave the way for advances in discovering extra- terrestrial life. It raises various unanswered questions which remain to be solved. Is it feasible to create a DNA with more than eight types of nucleotides? What kind of atmosphere would allow these unnatural bases to persist naturally? The possibilities are limitless! Such is the staggering capability of synthetic biology.

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