MIMIVIRE is the name French researchers have given to the immunity mechanism of mimivirus, and that they have now described in a new paper for Nature.
What is a mimivirus? What is viral immunity? What is life? What is CRISPR?
They have a diameter of about 0.5 mm (enough to be seen with an optical microscope) and the size of their genomes is comparable to bacteria: physical characteristics you really wouldn’t expect from typical viruses.
Didier Raoult, one of the authors, defends that mimivirus are alive. In fact, he argues they are a fourth domain of life (but other scientists don’t agree). This theory was spurred by the fact these mimivirus can be infected by other viruses (virophages, similar to bacteriophages that infect bacteria) – like a living organism.
So what did they discover?
With the ‘Live-or-not’ debate aside, the key finding in this paper is that a certain virophage is able to infect some mimiviruses and use them as a host, but not others. So, these giant virus have evolved a sort of immunity system, in a similar way to which bacteria have developed CRISPR to attack infecting phages and chop them up.
The resistant mimiviruses included sections of the attacking phage’s genetic material in its own genome. Not only that, these sections were located next to genes coding for enzymes which break down DNA. This is another parallel to how CRISPR works, whereby genetic material of previous infections (or attempted infection) are ‘remembered’ by the Host defense system.
Researchers still need to understand the precise mechanism of this viral immunity, but they are confident that will hold a lot of answers in the biology field. For example, the origin of these viruses – and perhaps even help the debate on whether viruses can be considered a part of the Tree of Life?
And not only that, but there is a lot of curiosity regarding potential technological applications of this new system. CRISPR was described only some years ago and is already hailed as the key biotechnology discovery of the century.
So will MIMIVIRE be the a second CRISPR, something completely different…or just a textbook curiosity?
Feature image credit: © Sergey Nivens (BigStock ID98726111)
Figure 1 credit: Levasseur et. al (2016) MIMIVIRE is a defence system in mimivirus that confers resistance to virophage. Nature (doi: 10.1038/nature17146)
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