Antivirus system found in giant mimiviruses

Giant mimiviruses defend themselves against foreign organisms using a system similar to CRISPR , as in bacteria and other microorganisms, found French researchers from the University of Aix-Marseille. They say that the presence of an active immune system in mimiviruses makes it possible to separate them into a separate supra-kingdom of organisms, along with eukaryotes, bacteria and archaea.

Mimiviruses are so large that they are visible in a conventional optical microscope. About 0.5 micrometers in size, they first appeared in front of scientists in 1992, when they infected an amoeba in a water tower. At the same time, the size of the mimivirus genome is larger than that of those same bacteria.

Unlike viruses, mimiviruses have genes for the production of amino acids and complex protein proteins - protein threads similar to flagella are made of them. A detailed study of the complex genome of the mimivirus is still ongoing.

Mimiviruses occupy an intermediate position between viruses and microbes, mimicking under the latter (hence the name).

Like prokaryotes (microbes), mimivirus is susceptible to attacks of viruses - virophages. French biologists found out in 2008. In 2014, the same group of scientists determined that the virophage - it was called Zamilon - affects only certain types of mimiviruses, but not others. After the defeat, the mimivirus loses the ability to make copies of itself.

Scientists have suggested that such infections can lead to the formation of a defense system of the CRISPR type.

Prokaryotes CRISPR is a database of short DNA fragments that correspond to phages and other harmful organisms. When a foreign DNA, a sample of which is present in the signature database, attacks a cell, specialized Cas enzymes are sent towards the intruder and break its DNA into pieces. By the way, now the CRISPR technique is used by geneticists as a way to edit the genome . It will be tested in public in 2017 .

To test their theory, French geneticists analyzed the genomes of 60 copies of the mimivirus. They searched for sequences that match the Zamilon virophage genome, that is, the signature of the antivirus system. It turned out that such signatures are present in the genome of mimiviruses that are resistant to infection. Then they found genes that encode the corresponding enzymes. In the end, for the final test, scientists blocked these genes, after which the mimivirus was infected with a virophage. This is clear evidence of the existence of the immune system in mimiviruses. She was named MIMIVIRE.


MIMIVIRE defense system

Scientific work published February 29, 2016 in the journal Nature ( doi: 10.1038 / nature17146 ), mirror .