American scientists have identified a viral protein that suppresses
activity of the CRISPR system-Cas13 working with RNA.
In addition, that the protein allows the phages to overcome bacterial system
immunity and multiply, potentially it can be used to control
the activity of CRISPR in
human cells, suggest the authors of the article in Science.
System CRISPR-Cas, which in recent
the time is actively used for editing of mammalian genomes, nature
is bacteria to protect against viruses (bacteriophages). The system is
an analog of adaptive immune system, which allows you to store ex
infection and re-appearance of the enemy to target the nuclease Cas against the alien
DNA or RNA. However, in the evolution of bacteriophages is produced
antiimpunity that allows them to infect bacteria, in spite of CRISPR.
One such evolutionary genetics above described of
Rockefeller University, new York, led by Luciano of Marraghini (Luciano A. Marraffini). They found literotica ϕLS46 (virus that
specializiruetsya on bacteria of the genus Listeria) is a small protein that inhibits the nuclease Саѕ13а in the cells of Listeria seeligeri. Similar
inhibitors of protein families Acr have already been found for Cas9, however, scientists first managed
to allocate this for Cas13,
and to reveal the mechanism of its action.
The genome of the phage is a DNA molecule, which
transcribed into RNA when injected into the cell. Protective protein Cas13 destroys
phage transcripts and inhibit the replication of the virus. It is also of interest
the ability to recognize RNA in mammalian cells — so Саѕ13а used for the destruction of
RNA viruses in human cells aimed off gene expression, and
also for the detection of molecules in vitroin
the method of SHERLOCK.
Therefore, the detection of an inhibitor of nucleases can be interesting not only from the point
of view of evolution, but also for biotechnology.
Researchers have isolated phages from the collection of strains
Listeria in the next experiment identified those that are able to infect Listeria seeligeri. Then
phage genome is found ϕLS46
have otsenival and found genes similar to the Acr from other CRISPR systems.
These genes turned out to be four, and to determine which of them suppresses
antiphage immunity, all four gene are individually expressed in cells
Listeria. Found thus the protein was named AcrVIA1 that indicates the ability
to inhibit CRISPR-like system, VIA which the nuclease Cas13a.
The known CRISPR-Cas9 a nuclease
recognizes and cuts DNA molecules due to the presence of short RNA primers (in
human cells it is the role of the rail molecule, or hidaway RNA). The nuclease
RNA molecules by a similar mechanism of action. Research activity and
structure of inhibitor in complex with target showed that it inhibits Recusou
Cas13a activity due to strong binding
the place where the nuclease interacts with the priming.
In addition, the new inhibitor was very strong. Earlier
was able to block nuclease activity only in large quantity,
is to suppress bacterial immunity required multiple
infection. However, inhibition AcrVIA1
was effective enough so that each phage particle can infect
bacterial cell and reproduce. The authors hope that this property
useful for activity control in Cas13a
About several ways to use Cas13a we have already mentioned, and here you can read about the method
edit RNAS with her.