important each, to understand the mechanisms under-
lying this genetic protection gate against external ag-
gressions.
their intracellular multiplication, important to remind
that this mechanism is highly specific, and very similar
to the multicellular adaptive immunity as of the dy-
namic and the conditions of activation.
Figure -1-
Genomic adaptive immunity in prokaryotes
(Horvath P, Barrangou R (January 2010). "CRISPR/Cas, the immune system of bacteria and archaea)
1. Acquisition phase
In this phase, the bacteria acquires the viral sequences
through the processing of the viral genome in the cy-
tosol captured from the penetration of a particle. Spe-
cialized proteins such as Cas 1 and Cas 2 are involved
in the capture, processing, and integration of the spac-
ers between the CRISPR loci arrays, which announces
the implementation of genetic adaptive immunity
against the virus, and the activation of the CRISPR loci
activation.
2. Loci transcription and Biogenesis
There isn’t much of an exception to standard DNA tran-
scription scheme in the rest of the process, the CRIS-
PR loci is transcribed to generate a pmRNA, this last,
with the intervention of another set of CAS proteins is
cleaved to form many pieces crRNA that can bind to the
endonucleases necessary to guide their lysis function.
Many enzymes are implicated in the process of viral
genome cleavage, CAS9 being the most studied among
them all.
3. Interference
After the two steps, a complex of an endonuclease with
a non-specific DNA cleavage function and a specific se-
quence crRNA is obtained, guaranteeing a high-level
recognition ability towards any viral products generat-
ed inside the cell in the course of the viral cycle. This
action requires the special binding between the crRNA
and the viral DNA sequence, with respect to the stan-
dard nucleic acids binding characteristics (basic com-
plementarity), that means that the crRNA work almost
like “tags” or markers that underlie where the endonu-
cleases need to cleave, assuring the destruction of the
viral DNA and protection of the cell from the results of
Figure -2-
CRISPR – CAS9 as an editing tool
Area of Interest
After these data about the function and the character-
istics of the CRISPR-CAS9 system, the spectrum of po-
tential applications appeared to be extremely large, for
it provides a high level of specificity for any action it
would be associated with. That means we can program
any locus in any genetic material of any cell we want,
provided that we acquire the corresponding DNA se-
quences and incorporate them as spacers, and instead
of lysis, we would be able through molecular engineer-
ing of the enzymatic part of the complex, to add, de-
lete and replace sequences which can lead to desired
modifications on the cellular level, or correction of an
alteration in a given pathology process. This can revo-
lutionize therapies as of its highly accurate, robust and
fundamental effect on the cell function, the genetic ed-
iting, once technologically mastered, can provide many
solutions and open paths towards understanding some
of our era’s most complex pathologies
Application examples
As explained above, the possibilities of such a technol-
ogy are unlimited with access to many domains.
1. Industrial genetic engineering
The genetic editing of the recombinant DNA sequences
can help raise the rates of expression and with it, the
production capacity, improve pharmacological char-
acteristics and decrease immunisation risks. All these
procedures are based on a vehicle (Plasmid usually)
that carries the operon to the bacterial genome, en-
hanced with promotors and localization sequences.
ReMed Magazine - Numéro 4
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