DNA bases were ‘rewritten’ by a tiny organism discovered in a pond

We may think that the rules of DNA are set in stone, but the genetic code of a microscopic organism found in a garden pond in Oxford, UK, has proven once again that science is always changing.

The discovery was completely unexpected, as Dr Jamie McGowan and a team of researchers from the Earlham Institute and the University of Oxford were initially working on a new way to sequence very small amounts of DNA, such as that found in single-celled organisms.

Looking for something to test their method, the team isolated a protist from a freshwater pond in Oxford University’s gardens. If you’re wondering what protists are on Earth, McGowan has a helpful explanation (or not, depending on how you look at it):

“The definition of protist is loose – it is basically any eukaryotic organism that is not an animal, plant or fungus,” McGowan said in his article. statement. “This is obviously very general, because protists are a very variable group.

“Some are closely related to animals, others are closely related to plants. There are hunters and prey, parasites and hosts, swimmers and sitters, there are those who have a varied diet while others photosynthesize. Basically, we can make very few generalizations.”

Analyzing the protist’s genome, McGowan discovered that it was not only an entirely new species; Hymenophoria sp. PL0344, but it also had a unique difference in its genetic code.

Takes us back to school

You may have learned about copying DNA and translating it into proteins in school, but only a little For a refresher by Technology networks He is never wrong.

DNA is like a recipe. Transcription is a bit like reading that recipe and copying it with some modifications – the transcript is RNA, where there is a U instead of a T. At the end of the sentence, we find a period and the DNA copy of this is the stop codon, which is a three-letter sequence that tells us where the gene ends. When RNA is translated into amino acids, the building blocks of protein, a stop codon tells the protein’s little cooks (also known as ribosomes) where to stop.

The stop codons TAA, TAG, and TGA are found in almost all organisms, and the first and second codons in particular are thought to be strongly linked, as one does not change without the other also changing.

“In almost every other case we know of, the TAA and TAG change in tandem,” McGowan said. “When they are not stop codons, they each specify the same amino acid.”

New genetic discovery

Hymenophoria sp. However, PL0344 bucks this trend: it is a ciliate, a type of water-dwelling protist that usually has changes in its DNA. In its genome, only TGA encodes a stop codon, and the natural twin TAA and TAG are translated into two different amino acids. There are also more copies of TGA in the protists’ genome than expected, which the researchers believe makes up for the lack of the other two stop codons.

“This is very unusual,” McGowan explained. “We’re not aware of any other case where these stop codons are linked to two different amino acids. It breaks some of the rules we thought we knew about gene translation, since these two codons were thought to be related to each other.”

Types of abnormalities researchers found Hymenophoria sp. PL0344 could serve as inspiration for future genetic discoveries.

“Scientists are trying to engineer new genetic codes – but they also exist in nature. There are wonderful things we can find, if we look for them.

“Or, in this case,” McGowan said, “when we’re not looking for them.”

The study is published in PLOS Genetics.