Traditional DNA is made up of four base pairs, A, C, G, and T. But the newly created genetic system is packed with eight - twice as many as would normally be found in self-replicating molecules. The new system was called "hachimoji", and what is most interesting - it may look like the building blocks of extraterrestrial life, that is, aliens. A new study published recently in Science describes hachimoji, which means "eight letters" in Japanese.
In addition to the four base pairs, this genetic system has four building blocks, which significantly increase the density of information compared to conventional DNA. The scientists submitting the work say the new system may be robust enough to support life - that is, support the processes required for Darwinian self-replication.
Alien DNA of eight letters
Let's make it clear right away that hachimoji is not an autonomous self-sustaining organism. Rather, it is a model of an alternative genetic structure required to sustain self-replicating life. On Earth, only RNA and DNA perform this function, but this does not mean that other options in space cannot exist. In fact, astrobiologists are very interested in this study, as it demonstrates another possible mechanism from which life could arise, evolve and become complex.
The authors of the study do not claim that hachimoji exists throughout the universe, but they do believe that it is possible to take and "imagine parallel processes," says Andrew Ellington, co-author of the new research and synthetic biologist at the University of Texas, Austin. "By carefully analyzing the roles of shape, size and structure in hachimoji DNA, in this work we expand our understanding of the types of molecules that could store information about extraterrestrial life in alien worlds."
In normal RNA and DNA, the combination of four base pairs allows the storage and transmission of genetic information. These four building blocks of DNA, or nucleotides, are composed of adenine, cytosine, guanine and thymine, or simply A, C, G, and T. In RNA, T is replaced by uracil (U). Basic bases encode amino acids, the fundamental building blocks of proteins.
Previous research has created synthetic DNA with four alternative letters in total and a system with two additional base pairs (six in total), but in the latest study, scientists have increased this number to eight.
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The four new letters, P, B, Z and S, are roughly similar in structure and functionality to regular DNA, according to new research; P and B are purine-like in function, while Z and S are pyrimidine-like. In tests, the genetic system has shown the ability to store and transmit information, essentially mimicking the molecular behavior of regular four-letter DNA. Importantly, hachimoji also satisfies Schrödinger's requirements, which define the Darwinian system of molecular evolution (the very same Schrödinger whose cat is neither alive nor dead). Schrödinger described four requirements for evolution: information storage, transmission, structural integrity, and a discernible physical form or structure.
“Hachimoji DNA can do everything that DNA does to sustain life. It pairs predictably, and the rules dictate its stability. Hachimoji DNA can be copied to create Hachimoji RNA, can synthesize proteins directly. Hachimoji RNA can have a selective phenotype (physical structure), and in this experiment, and a green fluorescent glow."
Laurie Haze, acting director of NASA's Planetary Science Division, praised the study: "The discovery of life is an increasingly important goal of NASA's planetary science missions, and this new work will help develop effective tools and experiments that will expand our search."
“This research is important because DNA has always been considered unique. For example, DNA is the only material with which we can design sequences with predictable stability,”says Floyd Romesberg, a geneticist at the Scripps Institute and author of a study with six synthetic pairs. “And as Steve Benner has shown, his new four letters also fulfill all aspects of this predictable stability. While there have been hints that things other than the four natural letters of DNA may have this property, this work truly demonstrates this for the first time.”
Romesberg also says that an important application of the eight-letter alphabet is in the control of molecular associations, that is, the ability to program the configuration of nucleotides. The eight-letter alphabet, he said, is inherently more specific than the four-letter alphabet.
“However, it will be useless if the stability of the eight-letter alphabet is not predictable or programmable,” says Romesberg. "By demonstrating this, Steve discovered new applications that are likely to appear in his laboratory soon."
The results of the work can lead not only to astrobiological consequences, but also leave a mark in the real world - for example, improve diagnostic equipment, environmental monitoring (like the detection of dangerous viruses), lead to the emergence of alternative information storage, proteins with added amino acids and new innovative drugs …
Ilya Khel