Scientists have discovered a microorganism with an unusual genetic code

The genetic code helps cells assemble proteins according to instructions written in DNA. In most living organisms, these rules are arranged in a similar way, but scientists have discovered a microorganism in which two standard signals for stopping protein assembly indicate different amino acids.

The finding shows that the genetic code may be more complex than previously thought. How researchers discovered the unusual mechanism and what it says about evolution is described in the Izvestia article.

An unexpected discovery in the Oxford reservoir

The study of the unusual genetic code was published in the journal PLOS Genetics. Scientists found it in the microorganism Oligohymenophorea sp. PL0344, found in a freshwater reservoir at the University of Oxford. Initially, the researchers tested a DNA sequencing method that allows them to study genetic material. However, when analyzing the genome, they noticed that the microorganism uses unusual rules for reading genetic information.

To understand the significance of the find, it is important to know how cells assemble proteins. Genetic information is read in small groups of three nucleotides, called codons. Most codons designate a specific amino acid from which a protein is built. Others act as stop signals: they tell the cell that it is time to complete the assembly.

Two stop signals began to indicate amino acids

Usually, the protein assembly stop is indicated by three codons: TAA, TAG, and TGA. In the detected microorganism, two of them have received a different meaning. TAA stands for the amino acid lysine, and TAG stands for glutamic acid. Only TGA has retained the usual stop signal function.

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How does a cell cope with unusual rules

Scientists have discovered special transport RNA genes in the genome. These molecules help the cell deliver the necessary amino acids during the protein assembly process. Their presence makes it possible to explain how the microorganism uses unusual codon values.

The researchers also found a large number of TGA codons immediately after the regions containing instructions for the proteins. Such signals can help stop assembly if the cell continues to read genetic information outside the desired area.

The genetic code of other ciliates is also different.

Unusual variants of the genetic code are found in other protozoa. In another study published in the journal PLOS Genetics, scientists described several such variants in ciliates. In the five species studied, the UAG codon, which usually serves as a stop signal, designated another amino acid, leucine or glutamine. At the same time, the UAA codon retained the stop function.

A comparison of the genomes showed that changes in the genetic code occurred independently in different evolutionary lines. This means that different groups of microorganisms could have arrived at similar changes in different ways. In this case, the mechanism found in Oligohymenophorea sp. PL0344 differs from the described variants in other ciliates.

What does the discovery say about evolution

The discovery of an unusual genetic code helps to understand how diverse the mechanisms by which cells create proteins can be. Comparing different microorganisms allows us to explore how these rules have changed over the course of evolution and why they remain similar in most living organisms.

Such knowledge can be useful for synthetic biology, a field in which scientists study the possibilities of changing the genetic code. However, the exact path of origin of the unusual system in the detected microorganism has not yet been established. The finding shows the existence of an alternative mechanism, but does not fully explain how and why it was formed.