The end of genes: Routine test reveals unique divergence in genetic code

Unexpectedly, researchers experimenting with a novel approach to single-cell sequencing have altered our knowledge of the principles governing genetics.

A protist's genome has shown a seemingly singular divergence in the DNA coding that indicates the end of a gene, indicating the need for more study to fully comprehend this varied collection of species.

The Earlham Institute's Dr. Jamie McGowan, a postdoctoral investigator, examined the genomic sequencing of a protist, a microscopic creature that was taken out of a freshwater pond at Oxford University Parks. PLoS Genetics published the research.

The goal of the project was to evaluate a pipeline for DNA sequencing that could handle very tiny quantities of DNA, like that found in a single cell. Dr. McGowan collaborated with a group of scientists from the Earlham Institute and the University of Oxford under the direction of Professor Thomas Richards.

However, while examining the genetic code, scientists discovered that the protist Oligohymenophorea sp. PL0344 is a unique species with an improbable alteration in the way its DNA is translated into proteins.

According to Dr. McGowan, "It's sheer luck we chose this protist to test our sequencing pipeline, and it just shows what's out there, highlighting just how little we know about the genetics of protists."

It is challenging to draw conclusions regarding prototists as a whole. There are bigger multicellular protists, such as kelp, slime molds, and red algae, but the majority are tiny, single-celled animals like amoebas, algae, and diatoms.

"The definition of a protist is loose—essentially it is any eukaryotic organism which is not an animal, plant, or fungus," stated Dr. McGowan. Protists are a highly diverse group, which explains why this is evidently quite general.

Some have closer ties to plants, while others have closer ties to animals. There are predators and prey, parasites and hosts, swimmers and observers, and some that photosynthesise while others have diverse diets. In essence, there aren't many generalizations we can draw."

A ciliate is Oligohymenophorea sp. PL0344. These swimming protists are present practically anywhere there is water and are visible under a microscope.

Genetic code alterations, such as the reassignment of one or more stop codons—the codons TAA, TAG, and TGA—occur often in ciliates. These three stop codons are used to indicate the end of a gene in almost all species.

Genetic code variations are exceedingly uncommon. The codons TAA and TAG almost invariably have the same translation among the few genetic code variations that have been documented to date, indicating that their evolution is related.

According to Dr. McGowan, "TAA and TAG change in tandem in almost every other case we know of." "When they aren't stop codons, they each specify the same amino acid."

DNA is comparable to a building's blueprint. It gives directions on what has to be done; it doesn't perform anything on its own. A gene has to be "read" and then translated into a molecule with a physical function in order for it to have an effect.

DNA must first be transcribed into an RNA copy in order for it to be read. The translation of this copy into amino acids, which are then assembled to form a three-dimensional molecule, occurs in a different region of the cell. The DNA start codon (ATG) is where the translation process begins, and it ends at a stop codon (usually TAA, TAG, or TGA).

Only TGA serves as a stop codon in Oligohymenophorea sp. PL0344, however Dr. McGowan discovered that the ciliate's DNA contains more TGA codons than anticipated, which are thought to make up for the absence of the other two. Rather, TAG designates glutamic acid while TAA indicates lysine.

"This is very unusual," stated Dr. McGowan. As far as we know, there isn't another instance in which these stop codons are connected to two distinct amino acids. Some laws of gene translation that we believed to be true are broken—these two codons were believed to be connected.

Although new genetic codes are being created by scientists, they can also be found in nature. If we search, we can find some very interesting stuff.

"Or, in this case, when we are not looking for them."

Provided by Earlham Institute