The CRISPR-Cas systems
The CRISPR-Cas systems are subdivided into Class 1 (Types
I, III and IV) and Class 2 (Types II, V, VI) [1]. Each system comprises of specific
endonuclease proteins (Cas) and a guide RNA molecule [2]. The guide RNA molecule is
responsible to guide the Cas protein to cut and remove foreign DNA in a
specific location [3].
The type II CRISPR/Cas9 system (Figure 4), are the simplest one among the three types and original for the genome editing technology. Its processes involved, firstly, the CRISPR array contains repeat regions separated by spacer regions derived from phage or invading pathogens. These are transcribed into a precursor (pre-crRNA). After that, the repeats hybridize with anti-repeat sequences within the tracrRNA. Then, the guide RNA molecule binds to a recombinant form of Cas9 protein that has DNA endonuclease activity (RNaseIII) and the resulting complex will cause target-specific double-stranded DNA cleavage [2,4].
References
The type II CRISPR/Cas9 system (Figure 4), are the simplest one among the three types and original for the genome editing technology. Its processes involved, firstly, the CRISPR array contains repeat regions separated by spacer regions derived from phage or invading pathogens. These are transcribed into a precursor (pre-crRNA). After that, the repeats hybridize with anti-repeat sequences within the tracrRNA. Then, the guide RNA molecule binds to a recombinant form of Cas9 protein that has DNA endonuclease activity (RNaseIII) and the resulting complex will cause target-specific double-stranded DNA cleavage [2,4].
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Figure 4. The process of type II CRISPR/Cas9 system [2].
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1. Makarova, K.S., Wolf, Y.I., Alkhnbashi,
O.S., Costa, F., Shah, S.A., Saunders, S.J., Barrangou, R., Brouns, S.J.J.,
Charpentier, E., Haft, D.H., Horvath, P., Moineau, S., Mojica, F.J.M., Terns,
R.M., Terns, M.P., White, M.F., Yakunin, A.F., Garrett, R.A., van der Oost, J.,
Backofen, R., Koonin, E.V., 2015. An updated evolutionary classification of
CRISPR-Cas systems. Nat Rev Micro 13, 722-736.
2. Oude Blenke, E., Evers, M.J., Mastrobattista, E.,
van der Oost, J., 2016. CRISPR-Cas9 gene editing: Delivery aspects and
therapeutic potential. J Control Release 244, 139-148.
3. https://www.broadinstitute.org/what-broad/areas-focus/project-spotlight/questions-and-answers-about-crispr
4. http://www.clontech.com/US/Products/Genome_Editing/CRISPR_Cas9/Resources/About_CRISPR_Cas9
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