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The giant virus found bacterial “immune system”

From own parasites mimivirus protected with the help of molecular-genetic systems, which, probably, once borrowed from bacteria.

The virus is so unique in nature that until now biologists are debating whether to read them alive: in themselves they represent only a molecular complex of proteins, nucleic acids and sometimes lipids, they have no metabolism and for reproduction viruses need to get into somebody’s cage.And once inside the bacteria or eukaryotic cell, they use the host’s molecular machines to make their own copies.

У гигантских вирусов нашли бактериальную «иммунную систему»
The mimivirus under the electron microscope. (AJC photo /


The genome of viruses is very small – naturally, because they literally come on all ready, when infecting a cell. Their origin and evolution remains a mystery. Someone believes that they have no relation to living organisms that it just enraged molecular complexes that existed at the dawn of life, or break free from the already formed cells, some people think that they can be included in the tree of life that they originate from the last common ancestor of all life on Earth, and that the first of the viruses had a more complex structure than their modern descendants.

Passions around of the virus has inflamed with new force when they were discovered giant viruses – mimivirus, megavirus, pandorabrowse and papovirus. Historically the first was the mimivirus, was found in the amoebae, and then he was in size the smallest of “giants”. However, compared to other viruses it is quite great: mimivirus particle diameter reaches the MIC, and to see quite a light microscope.

Mimivirus similar to some conventional viruses – in particular, smallpox – but mimivirus genes encoded enzymes required for the synthesis of amino acids and nucleotide bases of DNA, and a number of complex proteins. Genome size of mimivirus surpass not only common viruses, but some bacteria.

But this was not all – giant viruses have found their own virus parasites, the so-called virophage. They multiply in the same cells, and large viruses, the genome of virophage encodes some of the proteins needed to copy genetic molecules, but virophage uses in some of the molecular processes of the proteins of the virus-host.

It is known that different virophage prefer different “giants”, for example, veriag Sumilon affects the family Mimiviridae (i.e. mimivirus). And here Bernard La Scola (Bernard La Scola) and Didier Raoult (Didier Raoult) from the INSERM Institute, which in 2014 opened virophage Sumilon, thought that mimivirus may be a system of protection against the parasite. Indeed, it turned out that such a “viral virus” protection is, and that it is very similar to a similar system in bacteria called CRISPR.

Molecular-genetic system CRISPR/Cas is often referred to as a bacterial immune system, because with its help, the bacteria can store information on the virus and use it to protect from future infections. It works so: in the bacterial chromosome has a plot CRISPR, short for Clustered Regularly Interspaced Short Repeats are palindromic – “short palindromic repeats in DNA, regularly spaced groups.”

Repeats interspersed with other sequences, which are inserted into the chromosome of genome of viruses-bacteriophages. This is a bacterial “immune memory”. When appears in the cell of the foreign DNA, the bacterium removes the RNA copy of the recorded sequence and compares it with a stranger. If there is a match, it means that foreign DNA needs to be destroyed.

Of course, the entire procedure is done using special protein complexes – Cas-enzymes. (Of special interest to the system CRISPR/Cas emerged from the biotechnologists, when it became clear that with the help of Cas proteins can relatively easily edit the genome of, well, quite a big buzz about CRISPR/Cas rose in the previous year, when Chinese researchers have modified the genome of the human embryo.)

But back to mimivirus. When La Scola, Raul and their colleagues analyzed the genomes of dozens of strains of mimivirus, it was found that some sequences mimivirus DNA sequences coincide with their virophage – that is, it was as if the CRISPR counterparts in the bacterial chromosome. Those strains of mimivirus at which such matches were, proved to be resistant to the parasite.

In addition, mimivirus find genes proteins similar to enzymes Cas – they also destroyed foreign genetic material that matched with the sample that was recorded in “immune memory”. When such mimivirus proteins are blocked, the virus could not resist the attack of virophage. (Just in case I will specify that under attack here means the withdrawal molecular resources: virophage as if to entice the molecule, without which it is impossible ^ to gather your own proteins.) The results of experiments published in the article in Nature.

Some parts of the system CRISPR/Cas and there are other viruses, however, it is unclear whether she has them or just lies dormant. Most likely, the viral genome it came from bacteria – it is known that viruses are able to grab a host’s genes.

How exactly does “viral antiviral immunity”, whether it is similar in this sense to the usual bacterial anti-virus protection, or do they have differences, will show further research yet, again, we learned only that some viruses (mimivirus) can be effectively protected from viroflow using bacteriophages molecular genetic protective system. But, be that as it may, the evolutionary history of viruses in the light of new data becomes even more interesting.

According to the materials of Nature News.

Author: Cyril Stasevich

Source: nkj.EN

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