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Cas9 has been used often as a genome-editing tool. Cas9 has been used in recent developments in preventing viruses from manipulating hosts' DNA. Since the CRISPR-Cas9 was developed from bacterial genome systems, it can be used to target the genetic material in viruses. The use of the enzyme Cas9 can be a solution to many viral infections.
CRISPR/Cas9 was fused with specific enzymes that initially could only change C to T and G to A mutations and their reverse. This was accomplished eventually without requiring any DNA cleavage. [117] [118] [119] With the fusion of another enzyme, the base editing CRISPR-Cas9 system can also edit C to G and its reverse. [120]
It is far less effective at gene correction. Methods of base editing are under development in which a “nuclease-dead” Cas 9 endonuclease or a related enzyme is used for gene targeting while a linked deaminase enzyme makes a targeted base change in the DNA. [69] The most recent refinement of CRISPR-Cas9 is called Prime Editing.
Cas9 (or "CRISPR-associated protein 9") is an enzyme that uses CRISPR sequences as a guide to recognize and open up specific strands of DNA that are complementary to the CRISPR sequence. Cas9 enzymes together with CRISPR sequences form the basis of a technology known as CRISPR-Cas9 that can be used to edit genes within living organisms.
Complementary base pairing between the sgRNA and genomic DNA allows targeting of Cas9 or dCas9. A small guide RNA (sgRNA), or gRNA is an RNA with around 20 nucleotides used to direct Cas9 or dCas9 to their targets. gRNAs contain two major regions of importance for CRISPR systems: the scaffold and spacer regions.
CRISPR/Cas9 edits rely on non-homologous end joining (NHEJ) or homology-directed repair (HDR) to fix DNA breaks, while the prime editing system employs DNA mismatch repair. This is an important feature of this technology given that DNA repair mechanisms such as NHEJ and HDR, generate unwanted, random insertions or deletions (INDELs).
CRISPR-associated transposons have been harnessed for in vitro and in vivo gene editing at different targets, in different hosts, and with different payloads. All CAST components of the Tn6677 system from Vibrio cholerae have been combined into a single plasmid and confirmed to deliver up to 10kb transposons at near 100% efficiency. [ 16 ]
CRISPR RNA or crRNA is a RNA transcript from the CRISPR locus. [1] CRISPR-Cas (clustered, regularly interspaced short palindromic repeats - CRISPR associated systems) is an adaptive immune system found in bacteria and archaea to protect against mobile genetic elements , like viruses , plasmids , and transposons . [ 2 ]