The largest RNA virus ever detected

The discovery was a coincidence, as scientists were not looking for any viruses

. The Leiden University Medical Center (LUMC) and the Howard Hughes Medical Institute in the United States have discovered by chance an RNA virus with a record-sized genome. The virus does not appear to be pathogenic, but the discovery redefines the way experts view the evolution of viruses. The researchers published their findings in the scientific journal PLOS Pathogens

. This discovery was a coincidence, because scientists were not looking for any viruses. "Our American colleagues are studying how the tissue is recovering.They use a flatworm for this, whose body regrows if you cut a piece.Amir Saberi, a student at the master's degree, came across this unknown RNA virus," says the professor. Alexander Gorbalenya of the Department of Medical Microbiology.

Great Difference
When his American colleague Philip Newmark made contact with him he took him because of his expertise in the virus, he did not know what he had heard at early, says Gorbalenya. "The largest RNA virus known up to then had a genome of about 33,000 nucleotides, while the genome of this new virus had more than 41,000 nucleotides." This does not seem to be a big difference, but it is indeed the case. The 8,000 nucleotides are almost as long as the entire poliovirus genome.

Twice in 25 years
"The unexpected discovery of this virus brings considerable progress to our knowledge," says Gorbalenya. "Scientists are now discovering new viruses almost every hour, but in the last 25 years they have been twice as big as previously known RNA viruses, and even then there was a difference of less than 2,000 nucleotides. PhD student Anastasia Gulyaeva mapped the genome of the new virus with the help of computer models and concluded that it was a very special nidovirus.The virus belongs to the coronavirus family. SARS and MERS.

Evolution of viruses and life
This discovery is important because it informs scientists about the evolution of viruses and life.The length of the genome is strongly linked to the complexity of an organism.People and other organisms made up of cells use DNA to create a genome.In the early stages of evolution, organisms use RNA. RNA is a As a relatively fragile molecule, it has been replaced at a certain stage of its evolution – billions of years ago – by DNA. The discovery of this large RNA virus shows that this moment of transfer is not at 30 000 nucleotides, but at a minimum of 40 000 nucleotides.

Is the border now reached? "With this discovery, we now know for sure that nidoviruses have the ability to evolve into an even larger RNA genome, and we have only found the tip of the iceberg in terms of virus, I do not exclude the possibility that large RNA viruses are waiting to be discovered, "says Gorbalenya.

The publication "A planar nidovirus extends the boundaries or size of the RNA genome" can be found on the website of PLOS Pathogens.