Breaking Genetic Norms: The Codons of Oligohymenophorea sp. PL0344
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(Image Credit: Earlham Institute)
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August 6, 2024
Ela Selin Akgün
12th Grade
Isikkent High School
Dr. Jamie McGowan, a postdoctoral scientist at the Earlham Institute, analyzed the genome sequence of a microscopic organism—a protist—isolated from a freshwater pond at Oxford University Parks. Mcgowan was working on sequencing single cellular organisms and he came upon Oligohymenophorea sp. PL0344. This organism had a unique way of translating RNA codons into proteins. While examining the genetic structure of Oligohymenophorea sp. PL0344, Dr. McGowan discovered that, unlike most known organisms, this ciliate uses only TGA as a stop codon, causing a paradigm shift in genetics.
(Image Credit: The National Institute of Social Sciences)
To express the gene, cells undergo processes called “translation” and “transcription”. In translation, the gene is copied to produce an RNA transcript called messenger RNA (mRNA). Later on, mRNA is transcribed as amino acids in the ribosomes to produce different proteins for different purposes. During transcription, ribosomes use codons that correspond with a specific amino acid or stop signal during protein synthesis. Normally, these codons are considered universal, and changes are extremely rare. “TAA”, “TAG”, and “TGA” are the three stop codons most organisms use, including us humans. However, Oligohymenophorea sp. PL0344 is breaking norms by not using “TAA” and “TAG” as stop codons but rather coding for two different amino acids.
In other reported cases to this date, “TAA” and “TAG” are translated as the same amino acid when not used as stop codons. As Mcgowan explains, "In almost every other case we know of, TAA and TAG change in tandem. When they aren't stop codons, they each specify the same amino acid". However, Oligohymenophorea sp. PL0344 specifies TAA as lysine and TAG as glutamic acid. “This is extremely unusual”, Dr McGowan said. “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 – these two codons were thought to be coupled. Scientists attempt to engineer new genetic codes - but they are also out there in nature. There are fascinating things we can find if we look for them. Or, in this case, when we are not looking for them”.
Despite the advancement and technological developments in genomics, scientists still believe that many genetic anomalies are waiting to be discovered. Learning more about these anomalies and differences also helps scientists gain deeper insights into evolution and other organism groups, such as protists, about which we currently have limited information. Dr. McGowan's findings open new avenues for research into genetic coding mechanisms and evolutionary biology, providing valuable insights into how genetic diversity can arise and be maintained in various organisms.
Moreover, studying these genetic anomalies can shed light on the evolutionary history of protists and other less-understood organism groups. Protists, being a diverse and ancient group of microorganisms, hold many secrets about the early evolution of eukaryotes. Uncovering the genetic intricacies of species like Oligohymenophorea sp. PL0344 can offer clues about how complex life forms have evolved and adapted to various environments over millions of years.
Reference Sources
Mackenzie, R. (2023, October 27). Organism found in university pond rewrites the rules of DNA. Genomics Research From Technology
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McGowan, J., Kilias, E. S., Alacid, E., Lipscombe, J., Jenkins, B. H., Gharbi, K., ... & Swarbreck, D. (2023). Identification of a non-canonical
ciliate nuclear genetic code where UAA and UAG code for different amino acids. PLoS Genetics, 19(10), e1010913.
The end of genes: routine test reveals unique divergence in genetic code. (n.d.). Earlham Institute.
https://www.earlham.ac.uk/news/end-genes-routine-test-reveals-unique-divergence-genetic-code.
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