New 8-Letter DNA Rewrites the Genetic Code | SciShow News


[INTRO ♪] Last week, scientists announced that they’ve created a weird synthetic DNA in the lab. They added four new letters to the usual four, creating a molecule with an 8-letter code. Which is pretty freaking mind-blowing. Having an 8-letter code really expands DNA’s ability to store information so this synthetic DNA could change the way we keep data long-term. And it makes us realize that our DNA isn’t
really special. For billions of years, all life on this planet has stored its genetic information using molecules of DNA. Strands of DNA pair thanks to hydrogen bonds to form a long, spirally structure called a double helix. Each of those strands is made up of sequences of four different nitrogenous bases: adenine, guanine, cytosine, and thymine, or A, G, C, and T. And it’s the sequences in which these bases appear that forms the genetic code underlying life as we know it. And yeah, yeah, I know—you learned about all this stuff in biology class. But the researchers publishing last week in the journal Science kind of literally rewrote the genetic code. They made DNA with A, G, C, and T, but also with four new bases, which they called P, B, Z, and S. The researchers called the new DNA “hachimoji DNA,” from the Japanese words for “eight” and “letter.” In order to show that hachimoji DNA was legit and could really be used as a genetic code, the researchers had to be sure it could do three things: reliably form matching base pairs, keep its shape when mutations occur, and be read and translated into RNA. So they did lots of tests that showed that similar to how A pairs with T and C pairs with G, P likes to bond with Z and B wants to pair with S—so you end up with two complementary strands of DNA. And these bonds were reliable and stable no matter which other bases they were next to in the sequence. Then, they looked at the effect of the synthetic bases on the overall structure of DNA. One important criteria of DNA is that the
nucleotides need to all be the same size, so that they don’t disrupt the double helix. If swapping bases into different parts of the code caused the whole thing to collapse, it would be impossible to have mutations. And since mutations are the foundation of Darwinian evolution, life can’t really exist without them. So, the researchers created three crystal structures of hachimoji DNA with different sequences, and found that the synthetic nucleotides didn’t warp DNA’s famous double helix too much. And the last thing that they wanted to make sure of was that the enzymes responsible for translating DNA into RNA could actually read the darn thing. After all, there’s no point in storing information if no one knows how to read it, and DNA isn’t useful unless it can be put into action. But enzymes the researchers tried kept having trouble with the S base, because it has a slightly weird chemical structure that messes with the strength of one of the hydrogen bonds it forms with B. So the researchers looked through variants of the enzyme, and finally found one that could read all four of the synthetic bases and make an RNA strand when given the bases’ synthetic RNA counterparts. Which means that hachimoji DNA works! And beyond the gee whiz of it all, there’s good reason to get worked up about this new weird DNA. For one, it’s capable of storing so much
more information. If you only have four letters to record stuff
with, you need longer sequences of those letters to make enough different combinations to represent
different information. But if you have eight letters? All those snazzy combinations mean you can store more info in less space. And we’re not just talking about genetic data: scientists have been experimenting for decades with the idea of using DNA as a kind of hard drive. It’s already a pretty efficient data storage system, since it’s really tiny yet stable enough to have a shelf life of thousands of years—maybe up to a million under the right conditions. Already, researchers estimate that one gram of single-stranded DNA could hold a whopping 455 million terabytes of data. Hachimoji DNA could hold a lot more, depending on how the data is coded. The newfangled DNA could also have medical and biotech applications. For example, small strings of DNA can be used to create a kind of molecular probe called an aptamer. Based on the sequence, these aptamers can locate specific molecules—like, the compounds that are only found in or on cancer cells. And that means, they could help target medications, or light up tumors so doctors know what to remove. Previous work from this research group has shown that DNA aptamers with Z and P bases are even better probes because more base options allows for more specificity, so it’s likely hatchimoji DNA will be even better. And then, of course, there’s what this research says about life itself. I mean, it’s not that we’ve created alien life forms or anything like that. Hachimoji DNA isn’t self-sustaining and
it can’t exist outside the lab, so it’s not really life. The research was funded by NASA, though, in the hopes of better understanding what other life might look like if we were to find it somewhere out there in the universe. Because what hachimoji DNA tells us is that there isn’t something perfect and singular about the four bases we use. Life might have evolved some other way. DNA could have looked different. It didn’t—but it could have. Which is mostly a reminder that we have to keep our minds open when searching for alien life, because if DNA isn’t as special as we thought, a DNA test might not detect all living things. Thanks for watching this episode of SciShow News! Every Friday, we break down the latest science headlines so that you can stay up to date with the most important discoveries. And all week long we post episodes about the awesome universe we’re living in, so if you want to keep up with that, hit that little subscribe button! [OUTRO ♪]