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technology:dna-editing
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Table of Contents
CRISPR Cas9
Cas 9 enzyme has a sequence locator called the PAM. When the PAM finds a piece of DNA with its sequence, the enzyme unzips the adjacent DNA to see if it matches the guide-RNA. Matching DNA triggers the Cas 9 enzyme to double-strand-break (DSB) the DNA. A DSB is often not a clean break. Some nucleotides can be lost in the process.
The host DNA repair mechanisms come about to repair the DSB, and if a homologous DNA strand is around, it will be used as a template for repair. The homologous DNA can be provided as part of the technological payload, for the purpose of altering the genome.
Cas9 can also be engineered without DNA-cleaving and purposed for epigenome editing instead.
Zinc Finger
TALENS
Meganucleases
Site Specific Recombinases SSRs
“Relying on homology-directed-repair (HDR) for editing risks introducing indels or chromosomal translocations. Even with a precisely targeted nuclease, with HDR, “you’re at the mercy of the cell,” Stoddard observes. For editing without the unpredictability of HDR, he adds, watch for developments in site-specific recombinases (SSRs).” (Tachibana 2019)1)
However, it can take 100 days to prepare an SSR, whereas CRISPR Cas9 takes one day, so it is speedier for research.
technology/dna-editing.1575839973.txt.gz · Last modified: 2019/12/08 21:19 by marcos
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